Which of the following materials has the lowest temperature coefficient of resistance?
Answer: B
Constantan (copper-nickel alloy) has the lowest temperature coefficient of resistance, making it ideal for standard resistors
Q.342Easy
In a Wheatstone bridge, if P/Q = R/S, then the galvanometer shows zero deflection. This condition is called:
Answer: C
Both balance condition and null point refer to the same situation where no current flows through the galvanometer
Q.343Medium
A battery with EMF E and internal resistance r is connected to an external resistance R. What is the terminal voltage?
Answer: B
Terminal voltage V = E - Ir, where I = E/(R+r), so V = E - E·r/(R+r) = ER/(R+r)
Q.344Easy
Five resistors each of 5Ω are connected in parallel. The equivalent resistance is:
Answer: C
For parallel: 1/R_eq = 5×(51) = 1, so R_eq = 1Ω
Q.345Medium
A potentiometer wire of length 100 cm has resistance 10Ω. A standard cell of EMF 1.5V is balanced at 40 cm. What is the EMF of an unknown cell if balanced at 65 cm?
Answer: C
By potentiometer principle: E₁/E₂ = l₁/l₂, so E₂ = 1.5 × (4065) = 2.4375V ≈ 2.4V
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Q.346Easy
The specific resistance (resistivity) of a material depends on:
Answer: B
Resistivity is an intrinsic property dependent on the material's nature and temperature, not on the dimensions or electrical parameters
Q.347Medium
In a circuit, the current through a 10Ω resistor is 2A. If this resistor is replaced by 5Ω, and the rest of the circuit remains unchanged, the new current will be:
Answer: D
Current depends on both the resistor value and the rest of the circuit configuration (series/parallel). Without knowing the circuit configuration, it cannot be determined
Q.348Medium
A uniform wire of length L is cut into n equal parts. When connected in parallel, the equivalent resistance is:
Answer: A
Each part has resistance R/n. In parallel: 1/R_eq = n/(R/n) = n²/R, so R_eq = R/n²
Q.349Easy
The drift velocity of electrons in a conductor is of the order of:
Answer: B
Drift velocity is typically 10⁻⁴ to 10⁻³ m/s, much smaller than electron thermal velocity or speed of electrical signal
Q.350Medium
If the length of a conductor is doubled and the diameter is also doubled, what happens to its resistance?
Answer: B
R = ρL/A. New R = ρ(2L)/π(2r)² = ρ(2L)/(4πr²) = R/2
Q.351Medium
A 60W bulb and a 100W bulb are connected in series across a 200V supply. Which bulb glows brighter?
Answer: A
In series, same current flows through both. Power = I²R. The 60W bulb has higher resistance (rated at lower power), so it dissipates more power and glows brighter
Q.352Medium
An ammeter has a low resistance and a voltmeter has a high resistance. This is because:
Answer: A
Low resistance ammeter minimizes voltage drop in series. High resistance voltmeter draws negligible current in parallel, not affecting the original circuit
Q.353Hard
Which of the following best explains why semiconductor resistance decreases with increase in temperature?
Answer: C
In semiconductors, increased temperature promotes more electrons from valence to conduction band, increasing carrier concentration and decreasing resistance
Q.354Medium
Three cells of EMF 2V, 4V, and 3V with negligible internal resistance are connected in series, opposing each other. Net EMF is:
Answer: C
Taking one direction as positive: 2 + 4 - 3 = 3V or 2 - 4 + 3 = 1V. Net EMF = 1V (assuming standard configuration)
Q.355Hard
A battery of EMF 12V and internal resistance 2Ω is connected to a load resistance R. For maximum power transfer, R should be:
Answer: B
Maximum power transfer theorem: Load resistance equals internal resistance. R = r = 2Ω for maximum power
Q.356Hard
The electric field inside a copper conductor carrying current is approximately:
Answer: B
By Ohm's law in microscopic form: E = ρJ. Inside the conductor, electric field maintains the drift of electrons
Q.357Medium
A 100Ω resistor and a 200Ω resistor are connected in parallel, and this combination is in series with a 50Ω resistor. Total resistance is:
Answer: B
Parallel: 1/R_p = 1001 + 2001 = 2003, so R_p = 66.67Ω. Total = 50 + 66.67 = 116.67Ω
Q.358Easy
The resistance of a wire at 0°C is R₀. If its temperature coefficient is α, its resistance at temperature T is:
Answer: A
R_T = R₀(1 + αT), where T is temperature rise from reference point (0°C in this case)
Q.359Hard
When a superconductor is cooled below its critical temperature, its resistance becomes zero. What is the effect on current flowing through it when connected to a constant voltage source?
Answer: A
With R = 0, by I = V/R, current becomes infinite. In practice, voltage source cannot be maintained across a superconductor
Q.360Medium
A wire of length L and cross-sectional area A has resistivity ρ. If the wire is stretched to 2L without change in volume, what will be its new resistance?
Answer: A
When stretched to 2L, volume remains constant. New area A' = A/2. New resistance R' = ρ(2L)/(A/2) = 4ρL/A = 4R
