Question 251

Circuit Diagram:

Does the 15 A current source have any effect on the circuit?

Options:

A) Yes
B) No
C) Cannot be determined
D) Yes, only when the 10 V source is removed

Answer: B) No

Step-by-Step Solution:

Observe the circuit carefully.

The 15 A current source forms its own loop between the two top nodes. Its current circulates within that local path and does not alter the operation of the branch containing the 10 V source.

Therefore, the remainder of the circuit behaves independently of the 15 A current source.

Hence, the 15 A current source has no effect on the rest of the circuit.

Why?

The current supplied by an ideal current source follows the path available within its connected loop.

Since the current source is confined to its own loop, it does not contribute additional current to the remaining branches of the circuit.

Additional Note:

An ideal current source affects only the portion of the circuit to which it is directly connected. If it is isolated within a separate loop, its presence does not influence the current or voltage in the other parts of the circuit.

✔ Answer: B) No

Question 252

KVL is associated with:

Options:

A) Mesh Analysis
B) Nodal Analysis
C) Both Mesh and Nodal Analysis
D) Neither Mesh nor Nodal Analysis

Answer: A) Mesh Analysis

Step-by-Step Solution:

Kirchhoff's Voltage Law (KVL) states:

The algebraic sum of all voltages around any closed loop is zero.

Mesh analysis applies KVL to every independent loop in a circuit to determine the unknown mesh currents.

Therefore, KVL is directly associated with mesh analysis.

Additional Note:

KVL is mainly used in:

Series circuits
Loop analysis
Mesh analysis of planar networks

✔ Answer: A) Mesh Analysis

Question 253

KCL is associated with:

Options:

A) Mesh Analysis
B) Nodal Analysis
C) Both Mesh and Nodal Analysis
D) Neither Mesh nor Nodal Analysis

Answer: B) Nodal Analysis

Step-by-Step Solution:

Kirchhoff's Current Law (KCL) states:

The total current entering a node is equal to the total current leaving the node.

Nodal analysis applies KCL at each node to determine the unknown node voltages.

Therefore, KCL is directly associated with nodal analysis.

Additional Note:

Comparison of circuit analysis methods:

Analysis Method	Fundamental Law	Unknown Quantity
Mesh Analysis	Kirchhoff's Voltage Law (KVL)	Mesh Currents
Nodal Analysis	Kirchhoff's Current Law (KCL)	Node Voltages

✔ Answer: B) Nodal Analysis

Question 254

What will be the equivalent resistance if ten resistors of 10 Ω each are connected in series?

Options:

A) 100 Ω
B) 1 Ω
C) 0.1 Ω
D) 10 Ω

Answer: A) 100 Ω

Step-by-Step Solution:

In a series circuit, the equivalent resistance is the sum of all individual resistances.

Given:

Number of resistors = 10
Resistance of each resistor = 10 Ω

Equivalent resistance,

R = 10 × 10 = 100 Ω

Important Notes:

In a series circuit, resistances are added directly.
The equivalent resistance is always greater than the largest individual resistance.
The same current flows through every resistor connected in series.

✔ Answer: A) 100 Ω

Question 255

Resistivity of a wire depends on:

Options:

A) Length
B) Material
C) Cross-sectional area
D) All of the above

Answer: B) Material

Step-by-Step Solution:

Resistivity (ρ) is an intrinsic property of a material.

It depends only on:

Material
Temperature

It does not depend on the length or cross-sectional area of the conductor.

Important Notes:

Resistance: $R = \frac{ρ L}{A}$
Resistivity: Material property.
SI unit of resistivity = Ω·m (Ohm-metre).

✔ Answer: B) Material

Question 256

Which of the following is NOT equal to one watt?

Options:

A) Joule/second
B) Ampere/Volt
C) Ampere × Volt
D) Ampere² × Ohm

Answer: B) Ampere/Volt

Step-by-Step Solution:

Power is given by:

P = VI

Other equivalent expressions are:

P = I²R
P = V²/R
1 W = 1 J/s

However,

Ampere/Volt = Siemens (S), which is the unit of conductance, not power.

Important Notes:

Equivalent expressions for power are:

P = VI
P = I²R
P = V²/R
1 Watt = 1 Joule/second

SI unit of conductance = Siemens (S).

✔ Answer: B) Ampere/Volt

Question 257

Ohm's Law is NOT applicable to:

Options:

A) DC circuits
B) High currents
C) Small resistors
D) Semiconductors

Answer: D) Semiconductors

Step-by-Step Solution:

Ohm's Law is:

V = IR

It is applicable only to ohmic conductors, where resistance remains constant.

Semiconductors have a non-linear V-I characteristic, so Ohm's Law is not applicable.

Important Notes:

Examples of non-ohmic devices:

Diode
Transistor
Thermistor
LED

Ohm's Law is valid only when temperature and physical conditions remain constant.

✔ Answer: D) Semiconductors

Question 258

A wire has a resistance $R$ . If both its length and cross-sectional area are doubled, what will be its new resistance?

Options:

A) 4R
B) 2R
C) R
D) R/4

Answer: C) R

Step-by-Step Solution:

Using,

R = ρL/A

After doubling both length and area,

$R^{'} = \frac{ρ (2 L)}{2 A}$ $R^{'} = \frac{ρ L}{A} = R$

Therefore,

New resistance = R

Important Notes:

Resistance is directly proportional to length.
Resistance is inversely proportional to cross-sectional area.
If both length and area change by the same factor, the resistance remains unchanged.

✔ Answer: C) R

Question 259

The rating of a fuse wire is expressed in terms of:

Options:

A) Ohms
B) Mhos
C) Amperes
D) Watts

Answer: C) Amperes

Step-by-Step Solution:

A fuse is a protective device that melts when the current exceeds its rated value.

Since a fuse is designed to protect against excess current, its rating is specified in amperes (A).

For example:

5 A Fuse
10 A Fuse
16 A Fuse

Important Notes:

Fuse rating is always expressed in Amperes (A).
A fuse is connected in series with the circuit.
It protects electrical equipment from overcurrent and short circuits.

✔ Answer: C) Amperes

Question 260

For maximum power transfer, the internal resistance of the source should be:

Options:

A) Equal to the load resistance
B) Less than the load resistance
C) Greater than the load resistance
D) Zero

Answer: A) Equal to the load resistance

Step-by-Step Solution:

According to the Maximum Power Transfer Theorem,

Maximum power is delivered to the load when:

Load Resistance (RL) = Internal Resistance (Rs)

Therefore,

RL = Rs

Important Notes:

Maximum power transfer occurs when RL = Rs.
Under this condition, the efficiency is 50%.
This theorem is widely used in communication and electronic circuits.

✔ Answer: A) Equal to the load resistance

Question 261

Thevenin's theorem can be applied to networks containing:

Options:

A) Passive elements only
B) Active elements only
C) Linear elements only
D) All of these

Answer: D) All of these

Step-by-Step Solution:

Thevenin's theorem states that any linear two-terminal network can be replaced by an equivalent voltage source in series with an equivalent resistance.

The network may contain:

Passive elements (R, L, C)
Active elements (Voltage and Current Sources)
Linear dependent sources

Hence, it is applicable to all these networks.

Important Notes:

Thevenin equivalent consists of:
- Vth (Equivalent Voltage Source)
- Rth (Equivalent Resistance)
It simplifies circuit analysis when the load changes frequently.

✔ Answer: D) All of these

Question 262

Which of the following theorems helps in simplifying computations when the load across a circuit is varying?

Options:

A) Superposition Theorem
B) Norton's Theorem
C) Thevenin's Theorem
D) Maximum Power Transfer Theorem

Answer: C) Thevenin's Theorem

Step-by-Step Solution:

When the load connected to a circuit changes repeatedly, solving the entire network every time is time-consuming.

Thevenin's theorem replaces the original network with:

A single equivalent voltage source (Vth)
A series resistance (Rth)

Then, only the load resistance needs to be changed for further calculations.

Therefore, Thevenin's theorem greatly simplifies repeated calculations for varying loads.

Important Notes:

Thevenin's theorem is mainly used when the load varies.
It reduces a complex network to a simple equivalent circuit.
Norton's theorem provides an equivalent current source representation.

✔ Answer: C) Thevenin's Theorem

Note: Although the source you provided lists Option D, the correct theorem for simplifying calculations with changing load resistance is Thevenin's Theorem (Option C).

Question 263

When maximum power transfer takes place, the efficiency of power transfer is:

Options:

A) 100%
B) 75%
C) 50%
D) 25%

Answer: C) 50%

Step-by-Step Solution:

Maximum power transfer occurs when:

RL = Rs

Under this condition,

Power supplied by the source is divided equally between:

Source resistance
Load resistance

Therefore,

$η = \frac{P_{l o a d}}{P_{i n p u t}} \times 100$ $η = \frac{1}{2} \times 100 = 50 %$

Hence,

Efficiency = 50%

Important Notes:

Maximum Power Transfer Condition:
- RL = Rs
Maximum power transfer does not mean maximum efficiency.
Maximum possible efficiency is achieved when RL >> Rs.

✔ Answer: C) 50%

Question 264

The Superposition Theorem requires as many circuit solutions as there are:

Options:

A) Nodes
B) Sources
C) Nodes and Sources
D) Nodes, Sources, and Meshes

Answer: B) Sources

Step-by-Step Solution:

According to the Superposition Theorem,

Only one independent source is considered active at a time, while all other independent sources are replaced by their internal resistances.

If a circuit has:

3 independent sources → Solve 3 circuits
5 independent sources → Solve 5 circuits

Therefore, the number of circuit solutions equals the number of independent sources.

Important Notes:

Superposition applies only to linear circuits.
Voltage sources are replaced by short circuits.
Current sources are replaced by open circuits.
Dependent sources remain active during analysis.

✔ Answer: B) Sources

Question 265

Two wires A and B have the same cross-sectional area and are made of the same material. If the resistance of wire A is 600 Ω and the resistance of wire B is 100 Ω, how many times is wire A longer than wire B?

Options:

A) 6
B) 2
C) 4
D) 5

Answer: A) 6

Step-by-Step Solution:

The resistance of a wire is given by:

R = ρL/A

Since both wires have:

Same material (ρ is constant)
Same cross-sectional area (A is constant)

Therefore,

Resistance ∝ Length

$\frac{L_{A}}{L_{B}} = \frac{R_{A}}{R_{B}}$

Substituting the given values,

$\frac{L_{A}}{L_{B}} = \frac{600}{100} = 6$

Hence, wire A is 6 times longer than wire B.

Important Notes:

For the same material and same cross-sectional area:
- Resistance is directly proportional to length.
Formula:
- R = ρL/A

✔ Answer: A) 6

Question 266

When a low resistance is connected in parallel with a high resistance, the combined resistance is:

Options:

A) Always more than the high resistance
B) Always less than the low resistance
C) Always between the values of high and low resistance
D) Either lower or higher than the low resistance depending on the value of the high resistance

Answer: B) Always less than the low resistance

Step-by-Step Solution:

For resistors connected in parallel,

$\frac{1}{R_{e q}} = \frac{1}{R_{1}} + \frac{1}{R_{2}}$

The equivalent resistance of a parallel circuit is always less than the smallest resistor in the combination.

Therefore, when a low resistance is connected in parallel with a high resistance, the combined resistance is always less than the lower resistance.

Important Notes:

In a parallel circuit, equivalent resistance is always less than the smallest branch resistance.
In a series circuit, equivalent resistance is always greater than the largest resistance.

✔ Answer: B) Always less than the low resistance

Question 267

Two 100 W, 200 V lamps are connected in series across a 200 V supply. What is the power consumed by each lamp?

Options:

A) 25 W
B) 50 W
C) 100 W
D) 200 W

Answer: A) 25 W

Step-by-Step Solution:

Each lamp is rated:

Power = 100 W
Voltage = 200 V

First, find the resistance of each lamp.

Using,

$R = \frac{V^{2}}{P}$ $R = \frac{200^{2}}{100} = 400 Ω$

Since two identical lamps are connected in series,

$R_{T} = 400 + 400 = 800 Ω$

Circuit current,

$I = \frac{V}{R_{T}} = \frac{200}{800} = 0.25 A$

Power consumed by each lamp,

$P = I^{2} R$ $P = (0.25)^{2} \times 400$ $P = 0.0625 \times 400 = 25 W$

Hence, each lamp consumes 25 W.

Important Notes:

For identical lamps in series:
- Current is the same through each lamp.
- Each lamp receives only half the supply voltage.
Formula:
- P = I²R

✔ Answer: A) 25 W

Question 268

The factor which has the least effect on the voltage at the load end of a two-wire supply circuit is:

Options:

A) Length of the circuit
B) Whether the supply frequency is 25 Hz or 50 Hz
C) Amount of load on the circuit
D) Cross-sectional area of the circuit wires

Answer: B) Whether the supply frequency is 25 Hz or 50 Hz

Step-by-Step Solution:

The voltage drop in a two-wire supply circuit mainly depends on:

Length of the conductor
Load current
Cross-sectional area of the conductor

The supply frequency (25 Hz or 50 Hz) has very little effect on the voltage drop in a normal resistive two-wire distribution circuit.

Therefore, frequency has the least influence.

Important Notes:

Voltage drop increases with:

Increased conductor length.
Increased load current.
Reduced conductor cross-sectional area.

Approximate voltage drop formula:

$V_{d} = I R$

✔ Answer: B) Whether the supply frequency is 25 Hz or 50 Hz

Question 269

For a given line voltage, four identical heating coils will produce maximum heat when connected:

Options:

A) All in parallel
B) All in series
C) Two parallel pairs in series
D) One pair in parallel with the other two in series

Answer: A) All in parallel

Step-by-Step Solution:

Heat produced is proportional to electrical power.

Using,

$P = \frac{V^{2}}{R}$

For a constant supply voltage:

Lower equivalent resistance results in higher power.
A parallel connection gives the minimum equivalent resistance.

Therefore, connecting all four heating coils in parallel produces the maximum heat.

Important Notes:

For a constant voltage source:
- Parallel connection → Maximum power and heat.
- Series connection → Minimum power and heat.
Heating effect is proportional to:
- P = V²/R
- H = I²Rt

✔ Answer: A) All in parallel

Question 270

For current to flow, a circuit must be:

Options:

A) Isolated
B) Insulated
C) Complete
D) Protected

Answer: C) Complete

Step-by-Step Solution:

Electric current can flow only when there is a closed conducting path between the source terminals.

If the circuit is open or incomplete, electrons cannot complete their path, and no current flows.

Therefore, a complete (closed) circuit is necessary for current flow.

Important Notes:

Closed circuit: Current flows.
Open circuit: No current flows.
Current always flows from the source through a complete path and returns to the source.

✔ Answer: C) Complete

Question 271

If a live conductor of a public supply touches earth metal, what happens?

Options:

A) Supply voltage will increase.
B) Supply voltage will decrease.
C) No current will flow.
D) Current will flow to earth.

Answer: D) Current will flow to earth

Step-by-Step Solution:

When a live conductor comes into contact with the earth or an earthed metal body, a fault path is created.

Since the earth provides a low-resistance path, a large fault current flows from the live conductor to the ground.

This high current usually causes the fuse or circuit breaker to operate and disconnect the supply.

Important Notes:

Earthing provides a safe path for fault current.
Earthing helps prevent electric shock.
Fault current causes protective devices (Fuse/MCB) to trip.

✔ Answer: D) Current will flow to earth

Question 272

Electric shock is:

Options:

A) Always fatal
B) Never fatal
C) Sometimes fatal
D) Always disfiguring

Answer: C) Sometimes fatal

Step-by-Step Solution:

The severity of an electric shock depends on several factors, including:

Magnitude of current.
Duration of contact.
Path of current through the body.
Supply voltage.
Body resistance.

A small current may produce only a mild sensation, whereas a larger current passing through the heart can be fatal.

Therefore, an electric shock is sometimes fatal, but not always.

Important Notes:

Currents above 30 mA can be dangerous.
Currents above 100 mA may cause ventricular fibrillation and can be fatal.
Proper earthing and protective devices reduce the risk of electric shock.

✔ Answer: C) Sometimes fatal

Question 273

Kirchhoff's Voltage Law (KVL) is not valid for a non-linear network.

Options:

A) TRUE
B) FALSE
C) Both
D) None

Answer: B) FALSE

Step-by-Step Solution:

Kirchhoff's Voltage Law (KVL) states:

The algebraic sum of all voltages around any closed loop is zero.

KVL is based on the law of conservation of energy.

It is valid for both linear and non-linear circuits, provided the circuit satisfies the assumptions of lumped network analysis.

Therefore, the statement "KVL is not valid for a non-linear network" is false.

Important Notes:

KVL is based on the conservation of energy.
KVL applies to both linear and non-linear circuits.
Mesh analysis is based on KVL.
KCL is based on the conservation of charge.

✔ Answer: B) FALSE

Question 274

The material used for a fuse must have:

Options:

A) Low melting point and low specific resistance
B) Low melting point and high specific resistance
C) High melting point and low specific resistance

Answer: B) Low melting point and high specific resistance

Step-by-Step Solution:

A fuse is a protective device that melts when excessive current flows through it.

For effective operation, the fuse material should have:

Low melting point, so it melts quickly during overload or short circuit.
High specific resistance (high resistivity), so it generates sufficient heat even with a small length of wire.

Hence, the correct choice is low melting point and high specific resistance.

Important Notes:

Fuse is always connected in series with the load.
It protects the circuit against overload and short circuit.
Common fuse materials are lead-tin alloy, tin, and silver.

✔ Answer: B) Low melting point and high specific resistance

Question 275

Which of the following statements regarding a capacitor is NOT true?

Options:

A) DC cannot flow through it.
B) AC can flow through it.
C) Current flows when a capacitor is connected for the first time across a battery.
D) Slight moisture increases its capacitance.

Answer: D) Slight moisture increases its capacitance.

Step-by-Step Solution:

A capacitor behaves differently for DC and AC:

It blocks DC after it is fully charged.
It allows AC to pass because the capacitor continuously charges and discharges.
When first connected to a DC source, a charging current flows until the capacitor becomes fully charged.

However, moisture does not increase the capacitance. Instead, moisture generally degrades the insulation, increases leakage current, and may reduce the reliability of the capacitor.

Therefore, option D is the incorrect statement.

Important Notes:

Capacitor blocks steady DC.
Capacitor offers capacitive reactance to AC.
Capacitive reactance:

$X_{C} = \frac{1}{2 π f C}$

As frequency increases, capacitive reactance decreases.

✔ Answer: D) Slight moisture increases its capacitance.

Question 276

A short circuit is one that:

Options:

A) Uses short pieces of wire.
B) Goes only a short distance.
C) Is used for dimming light.
D) Offers a very low resistance path for current to flow.

Answer: D) Offers a very low resistance path for current to flow

Step-by-Step Solution:

A short circuit occurs when a very low-resistance path is created between two points of different potential.

Since the resistance is almost zero,

$I = \frac{V}{R}$

The current becomes extremely large, which can damage equipment and create fire hazards.

Therefore, a short circuit is a path having very low resistance.

Important Notes:

Short circuit → Very low resistance.
Very high fault current flows.
Protective devices like Fuse, MCB, and MCCB disconnect the supply during a short circuit.

✔ Answer: D) Offers a very low resistance path for current to flow

Question 277

A parallel circuit is one that has:

Options:

A) All elements connected end-to-end.
B) The same current flowing through all elements.
C) All elements connected across the power supply so that removing one element does not stop the others from working.
D) All elements placed side by side.

Answer: C) All elements connected across the power supply so that removing one element does not stop the others from working

Step-by-Step Solution:

In a parallel circuit:

Every component is connected directly across the supply.
Each branch receives the full supply voltage.
If one branch is disconnected or fails, the remaining branches continue to operate.

Therefore, option C correctly describes a parallel circuit.

Important Notes:

Properties of a parallel circuit:

Voltage is the same across all branches.
Current divides among the branches.
Equivalent resistance is less than the smallest branch resistance.
Failure of one branch does not affect the others.

✔ Answer: C) All elements connected across the power supply so that removing one element does not stop the others from working

Question 278

The usual value of the surge impedance of a telephone line is:

Options:

A) 600 Ω
B) 500 Ω
C) 75 Ω
D) 100 Ω

Answer: C) 75 Ω

Step-by-Step Solution:

Surge impedance (or characteristic impedance) is the impedance offered by a transmission line to a travelling wave.

For telephone and communication systems, one of the commonly used characteristic impedance values is 75 Ω.

Hence, the correct answer is 75 Ω.

Important Notes:

Common characteristic impedances:

50 Ω – RF communication systems.
75 Ω – Television and communication cables.
600 Ω – Audio communication circuits (historical standard).

✔ Answer: C) 75 Ω

Question 279

In mesh analysis of a network, all the mesh currents must necessarily be either clockwise or anticlockwise.

Options:

A) TRUE
B) FALSE
C) Both
D) None

Answer: A) TRUE

Step-by-Step Solution:

In mesh analysis, the direction of mesh currents is assumed before writing the KVL equations.

For convenience and consistency, all mesh currents are generally assumed to flow in the same direction, either:

All clockwise, or
All anticlockwise.

If the assumed direction is opposite to the actual current direction, the calculated current will simply have a negative sign.

Therefore, the statement is TRUE.

Important Notes:

Mesh analysis is based on Kirchhoff's Voltage Law (KVL).
Mesh currents are assumed before solving the circuit.
A negative value indicates the actual current flows opposite to the assumed direction.

✔ Answer: A) TRUE

Question 280

Which of the following remains the same throughout all parts of a series circuit?

Options:

A) Voltage
B) Power
C) Resistance
D) Current

Answer: D) Current

Step-by-Step Solution:

In a series circuit, all components are connected one after another, forming a single path for the flow of current.

Since there is only one path, the same current flows through every component in the circuit.

However:

Voltage is divided among the components.
Power dissipated depends on the resistance of each component.
Total resistance is the sum of all resistances.

Therefore, the quantity that remains the same throughout the series circuit is current.

Important Notes:

In a series circuit:
- Current is the same throughout the circuit.
- Voltage divides across the resistors.
- Total resistance is the sum of all resistances.
Formula:
- Rₜ = R₁ + R₂ + R₃ + ...

✔ Answer: D) Current

Question 281

The resistance of the windings of a generator is known as:

Options:

A) Generated resistance
B) Field resistance
C) Internal resistance
D) Terminal resistance

Answer: C) Internal resistance

Step-by-Step Solution:

Every generator has windings made of conducting material such as copper.

These windings possess inherent electrical resistance, known as the internal resistance of the generator.

This resistance causes:

Internal voltage drop.
Copper losses (I²R losses).
Reduced terminal voltage under load.

Therefore, the resistance of the generator windings is called internal resistance.

Important Notes:

Internal resistance causes:
- Voltage drop inside the generator.
- Power loss due to heating.
Terminal voltage is given by:

$V = E - I R$

where:

E = Generated EMF
I = Load current
R = Internal resistance

✔ Answer: C) Internal resistance

Question 282

When resistance is added to a circuit having a constant supply voltage, the current is:

Options:

A) Reduced in the same proportion
B) Increased in the same proportion
C) Unaltered
D) Made fluctuating

Answer: A) Reduced in the same proportion

Step-by-Step Solution:

According to Ohm's Law,

$I = \frac{V}{R}$

If the supply voltage V remains constant and the resistance R increases, then the current I decreases.

Thus, adding more resistance to the circuit reduces the current.

Example:

If,

Voltage = 100 V
Initial Resistance = 10 Ω

Current,

$I = \frac{100}{10} = 10 A$

If the resistance is doubled to 20 Ω,

$I = \frac{100}{20} = 5 A$

The current becomes half.

Important Notes:

Ohm's Law:

$V = I R$

For constant voltage:
- Resistance ↑ ⇒ Current ↓
- Resistance ↓ ⇒ Current ↑
Current is inversely proportional to resistance.

✔ Answer: A) Reduced in the same proportion

Question 283

One ampere is the current which, if maintained in two straight parallel conductors of infinite length and negligible cross-sectional area, placed 1 m apart in vacuum, produces a force of:

Options:

A) $2 \times 10^{- 7}$ N per metre length
B) 1 N per metre length
C) $1 \times 10^{- 7}$ N per metre length
D) $2 \times 10^{7}$ N per metre length

Answer: A) $2 \times 10^{- 7}$ N per metre length

Step-by-Step Solution:

The classical SI definition of one ampere states:

One ampere is the constant current which, when maintained in two straight, parallel conductors of infinite length and negligible cross-section placed 1 metre apart in vacuum, produces a force of:

$2 \times 10^{- 7} N per metre$

Therefore, the correct answer is:

$2 \times 10^{- 7} N/m$

Important Notes:

Distance between conductors = 1 m
Medium = Vacuum
Force produced = $2 \times 10^{- 7}$ N/m
This is the classical SI definition of the ampere.

✔ Answer: A) $2 \times 10^{- 7}$ N/m

Question 284

Ohm's Law is applicable to:

Options:

A) Semiconductors
B) Vacuum tubes
C) Electrolytes
D) None of these

Answer: D) None of these

Step-by-Step Solution:

Ohm's Law is applicable only to ohmic conductors, where the voltage is directly proportional to the current.

The following are non-ohmic devices:

Semiconductors
Vacuum tubes
Electrolytes

Their resistance changes with voltage, current, or temperature.

Therefore, Ohm's Law is not applicable to any of these.

Important Notes:

Ohm's Law is valid only when:

Temperature remains constant.
Physical conditions remain unchanged.
The conductor exhibits a linear V-I characteristic.

Examples of ohmic conductors:

Copper
Aluminium
Silver

✔ Answer: D) None of these

Question 285

A wire of length $l$ and circular cross-sectional radius $r$ has a resistance $R$ . Another wire of the same material has a cross-sectional radius $2 r$ . What should be its length to have the same resistance $R$ ?

Options:

A) $2 l$
B) $l$
C) $4 l$
D) $l / 2$

Answer: C) $4 l$

Step-by-Step Solution:

Resistance is given by:

$R = \frac{ρ L}{A}$

Area of the first wire,

$A_{1} = π r^{2}$

Area of the second wire,

$A_{2} = π (2 r)^{2} = 4 π r^{2}$

Since both wires have the same resistance,

$\frac{ρ L_{1}}{A_{1}} = \frac{ρ L_{2}}{A_{2}}$

Substituting,

$\frac{L_{1}}{π r^{2}} = \frac{L_{2}}{4 π r^{2}}$ $L_{2} = 4 L_{1}$

Hence,

$L_{2} = 4 l$

Important Notes:

Resistance is directly proportional to length.
Resistance is inversely proportional to cross-sectional area.
If radius doubles, area becomes 4 times.

✔ Answer: C) $4 l$

Question 286

With an increase in temperature, the temperature coefficient of resistance:

Options:

A) Remains unaffected
B) Increases
C) Decreases
D) Is uncertain

Answer: C) Decreases

Step-by-Step Solution:

The temperature coefficient of resistance (α) is not perfectly constant over a wide temperature range.

For metallic conductors, its value gradually decreases as the temperature increases.

Therefore, with increasing temperature, the temperature coefficient decreases.

Important Notes:

For metals:
- Resistance increases with temperature.
- Temperature coefficient is positive.
The value of α is approximately constant only over a limited temperature range.

✔ Answer: C) Decreases

Question 287

The values of the temperature coefficient of resistance of a given conductor are:

Options:

A) The same at different temperatures
B) Higher at higher temperatures
C) Different at different temperatures
D) None of the above

Answer: C) Different at different temperatures

Step-by-Step Solution:

The temperature coefficient of resistance changes slightly with temperature.

Hence, its value is not exactly the same at different temperatures.

Therefore, the temperature coefficient is different at different temperatures.

Important Notes:

Temperature coefficient depends on:
- Material
- Temperature
Manufacturers generally specify its value at 20°C.

✔ Answer: C) Different at different temperatures

Question 288

Temperature coefficient of resistance is defined as:

Options:

A) Increase in resistance per ohm per °C
B) Increase in resistance per °C
C) Decrease in resistance per ohm per °C
D) Ratio of decrease in resistance per °C to the resistance at 0°C

Answer: A) Increase in resistance per ohm per °C

Step-by-Step Solution:

The temperature coefficient of resistance (α) is defined as:

The increase in resistance per ohm of original resistance per degree Celsius rise in temperature.

Mathematically,

$α = \frac{R - R_{0}}{R_{0} (T - T_{0})}$

where:

R₀ = Resistance at reference temperature
R = Resistance at temperature T

Important Notes:

Unit of temperature coefficient:

$^{\circ} C^{- 1}$

Formula for resistance at temperature T:

$R = R_{0} [1 + α (T - T_{0})]$

Metals have a positive temperature coefficient.
Insulators and semiconductors generally have a negative temperature coefficient.

✔ Answer: A) Increase in resistance per ohm per °C

Question 289

The equivalent resistance of two resistors connected in parallel is 12 Ω. If one resistor breaks (opens), the effective resistance becomes 18 Ω. What is the resistance of the broken resistor?

Options:

A) 48 Ω
B) 18 Ω
C) 36 Ω
D) 24 Ω

Answer: C) 36 Ω

Step-by-Step Solution:

Given:

Equivalent resistance in parallel, R = 12 Ω
After one resistor breaks, the remaining resistance is 18 Ω

Hence,

One resistor is:

R₁ = 18 Ω

Let the broken resistor be R₂.

Using the parallel resistance formula,

\frac{1}{R} = \frac{1}{R_{1}} + \frac{1}{R_{2}}

Substitute the values,

\frac{1}{12} = \frac{1}{18} + \frac{1}{R_{2}}

\frac{1}{R_{2}} = \frac{1}{12} - \frac{1}{18}

Taking LCM = 36,

\frac{1}{R_{2}} = \frac{3 - 2}{36}

\frac{1}{R_{2}} = \frac{1}{36}

Therefore,

R_{2} = 36 Ω

Hence, the resistance of the broken wire is 36 Ω.

Important Notes:

Parallel resistance formula:

\frac{1}{R} = \frac{1}{R_{1}} + \frac{1}{R_{2}}

The equivalent resistance of a parallel circuit is always less than the smallest resistor.
If one branch opens, only the remaining branch contributes to the circuit resistance.

✔ Answer: C) 36 Ω

Question 290

When one branch of a parallel circuit becomes open, the current drawn from the supply will:

Options:

A) Reduce
B) Increase
C) Remain the same
D) Uncertain

Answer: A) Reduce

Step-by-Step Solution:

In a parallel circuit,

Opening one branch removes one current path.
The equivalent resistance of the circuit increases.
According to Ohm's Law,

I = \frac{V}{R}

As the equivalent resistance increases, the total current drawn from the supply decreases.

Therefore, the supply current is reduced.

Important Notes:

Opening one parallel branch:
- Increases equivalent resistance.
- Decreases total current.
- Other healthy branches continue to operate normally.
Parallel circuits provide multiple current paths.

✔ Answer: A) Reduce

Question 291

For both series and parallel circuits, which of the following quantities is always additive?

Options:

A) Resistances
B) Powers
C) Currents
D) Voltage drops

Answer: B) Powers

Step-by-Step Solution:

The total power consumed in any electrical circuit is the sum of the powers consumed by all individual components.

Whether the resistors are connected in series or parallel,

P_{T} = P_{1} + P_{2} + P_{3} + \dots

Thus, power is always additive.

Important Notes:

Series circuit:
- Resistances are additive.
- Current remains the same.
- Voltage divides.
Parallel circuit:
- Voltage remains the same.
- Currents are additive.
- Equivalent resistance decreases.
Power is additive in both series and parallel circuits.

✔ Answer: B) Powers

Question 292

The heating effect of electric current is used in:

Options:

A) Electric furnaces
B) Geysers
C) Electric irons
D) All of the above

Answer: D) All of the above

Step-by-Step Solution:

The heating effect of electric current (Joule heating) occurs when current flows through a conductor, producing heat.

This principle is used in:

Electric furnaces
Electric geysers
Electric irons

All these appliances convert electrical energy into heat energy.

Hence, the correct answer is All of the above.

Note: The source answer "Vacuum cleaners" appears to be a printing error. Vacuum cleaners mainly use the motor effect, whereas electric furnaces, geysers, and irons operate on the heating effect.

Important Notes:

Heating effect is based on Joule's Law.
Heat produced:

$H = I^{2} R t$

Applications:

Electric iron
Room heater
Electric kettle
Geyser
Toaster
Electric furnace

✔ Answer: D) All of the above

Question 293

A 100 W bulb is connected in series with a room heater. If the 100 W bulb is replaced by a 40 W bulb, the heater output will:

Options:

A) Increase
B) Decrease
C) Remain the same
D) Cannot be determined

Answer: B) Decrease

Step-by-Step Solution:

For bulbs of the same rated voltage,

$R = \frac{V^{2}}{P}$

A 40 W bulb has a higher resistance than a 100 W bulb.

When connected in series with the heater:

Total circuit resistance increases.
Current through the circuit decreases.
Heater power,

$P = I^{2} R$

Since current decreases, the heater output also decreases.

Important Notes:

Lower wattage bulb ⇒ Higher resistance.
In a series circuit:
- Current is the same through all components.
- Increasing total resistance reduces current.
Heater output depends on I²R.

✔ Answer: B) Decrease

Question 294

An ideal voltage source should have:

Options:

A) Zero source resistance
B) Infinite source resistance
C) Terminal voltage proportional to current
D) Terminal voltage proportional to load

Answer: A) Zero source resistance

Step-by-Step Solution:

An ideal voltage source maintains a constant terminal voltage regardless of the load current.

To achieve this,

Internal resistance must be zero.

Thus,

$V_{t e r m i n a l} = E$

for every load.

Important Notes:

Properties of an ideal voltage source:

Internal resistance = 0 Ω
Terminal voltage remains constant.
Can supply any amount of current (ideal assumption).

✔ Answer: A) Zero source resistance

Question 295

For a voltage source, the terminal voltage:

Options:

A) Is equal to the source EMF.
B) Cannot exceed the source EMF.
C) Is always lower than the source EMF.
D) Is higher than the source EMF.

Answer: B) Cannot exceed the source EMF

Step-by-Step Solution:

The terminal voltage of a practical voltage source is

$V = E - I R$

where:

E = Source EMF
I = Load current
R = Internal resistance

Thus,

On no-load:

$V = E$

On load:

$V < E$

Therefore, the terminal voltage cannot exceed the source EMF.

Important Notes:

No-load condition:

$V = E$

Loaded condition:

$V = E - I R$

Internal resistance causes voltage drop.

✔ Answer: B) Cannot exceed the source EMF

Question 296

A constant voltage source is:

Options:

A) Active and bilateral
B) Passive and bilateral
C) Active and unilateral
D) Passive and unilateral

Answer: A) Active and bilateral

Step-by-Step Solution:

A voltage source is an active element because it supplies electrical energy to the circuit.

An ideal voltage source can operate regardless of the direction of current flow, making it bilateral.

Hence, it is classified as an active bilateral element.

Important Notes:

Active elements:
- Voltage source
- Current source
Passive elements:
- Resistor
- Inductor
- Capacitor
Bilateral elements behave the same in either direction of current flow.

✔ Answer: A) Active and bilateral

Question 297

An ideal current source has zero:

Options:

A) Internal conductance
B) Internal resistance
C) Voltage on no load
D) Ripple

Answer: A) Internal conductance

Step-by-Step Solution:

An ideal current source supplies constant current independent of the load.

Its internal resistance is infinite.

Since conductance is the reciprocal of resistance,

$G = \frac{1}{R}$

$R = \infty$

then

$G = 0$

Therefore, an ideal current source has zero internal conductance.

Important Notes:

Properties of an ideal current source:

Internal resistance = ∞
Internal conductance = 0
Delivers constant current regardless of load resistance.

✔ Answer: A) Internal conductance

Question 298

An active element is:

Options:

A) Resistor
B) Inductor
C) Current Source
D) All of these

Answer: C) Current Source

Step-by-Step Solution:

An active element is a component that can supply energy to an electrical circuit.

Among the given options:

Resistor dissipates energy as heat.
Inductor stores energy temporarily in its magnetic field.
Current Source supplies electrical energy to the circuit.

Therefore, the current source is an active element.

Important Notes:

Active elements: Voltage source, Current source.
Passive elements: Resistor, Inductor, Capacitor.
Active elements are capable of delivering power to a circuit.

✔ Answer: C) Current Source

Question 299

The terminals across a current source are __________ when the current source is to be neglected.

Options:

A) Open-circuited
B) Short-circuited
C) Replaced by a capacitor
D) Replaced by a source resistance

Answer: A) Open-circuited

Step-by-Step Solution:

When applying Superposition Theorem, only one independent source is kept active at a time.

To deactivate a source:

Voltage Source → Replace with a short circuit.
Current Source → Replace with an open circuit.

Therefore, when a current source is neglected, its terminals are open-circuited.

Important Notes:

Voltage Source OFF → Short Circuit
Current Source OFF → Open Circuit
Dependent (controlled) sources are not turned off during superposition.

✔ Answer: A) Open-circuited

Question 300

A bilateral element is:

Options:

A) Resistor
B) Inductor
C) Capacitor
D) All of these

Answer: D) All of these

Step-by-Step Solution:

A bilateral element behaves the same regardless of the direction of current flow or the polarity of the applied voltage.

The following are bilateral elements:

Resistor
Inductor
Capacitor

Their electrical characteristics remain unchanged when the direction of current is reversed.

Hence, all the given elements are bilateral.

Important Notes:

Bilateral Elements:

Resistor (R)
Inductor (L)
Capacitor (C)

Unilateral Elements:

Diode
Transistor
SCR
Zener Diode

A bilateral element has the same V-I characteristic in both directions.

2000 Basic Electrical Engineering Fully Solved MCQs-6

Question 251

Answer: B) No

Step-by-Step Solution:

Why?

Additional Note:

Question 252

Answer: A) Mesh Analysis

Step-by-Step Solution:

Additional Note:

Question 253

Answer: B) Nodal Analysis

Step-by-Step Solution:

Additional Note:

Question 254

Answer: A) 100 Ω

Step-by-Step Solution:

Important Notes:

Question 255

Answer: B) Material

Step-by-Step Solution:

Important Notes:

Question 256

Answer: B) Ampere/Volt

Step-by-Step Solution:

Important Notes:

Question 257

Answer: D) Semiconductors

Step-by-Step Solution:

Important Notes:

Question 258

Answer: C) R

Step-by-Step Solution:

Important Notes:

Question 259

Answer: C) Amperes

Step-by-Step Solution:

Important Notes:

Question 260

Answer: A) Equal to the load resistance

Step-by-Step Solution:

Important Notes:

Question 261

Answer: D) All of these

Step-by-Step Solution:

Important Notes:

Question 262

Answer: C) Thevenin's Theorem

Step-by-Step Solution:

Important Notes:

Question 263

Answer: C) 50%

Step-by-Step Solution:

Important Notes:

Question 264

Answer: B) Sources

Step-by-Step Solution:

Important Notes:

Question 265

Answer: A) 6

Step-by-Step Solution:

Important Notes:

Question 266

Answer: B) Always less than the low resistance

Step-by-Step Solution:

Important Notes:

Question 267

Answer: A) 25 W

Step-by-Step Solution:

Important Notes:

Question 268

Answer: B) Whether the supply frequency is 25 Hz or 50 Hz

Step-by-Step Solution:

Important Notes:

Question 269

Answer: A) All in parallel

Step-by-Step Solution:

Important Notes:

Question 270

Answer: C) Complete

Answer: A) $2 \times 10^{- 7}$ N per metre length

Answer: C) $4 l$