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.62Medium
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.63Medium
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.64Hard
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.65Medium
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)
Advertisement
Q.66Hard
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.67Hard
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.68Medium
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.69Easy
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.70Hard
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.71Medium
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
Q.72Easy
Two resistances of 3Ω and 6Ω are connected in parallel. The equivalent resistance is:
Answer: A
For parallel: 1/Rₑq = 31 + 61 = 63 = 21, so Rₑq = 2Ω
Q.73Medium
In a Wheatstone bridge, if P/Q = R/S, then the current through the galvanometer is:
Answer: B
The bridge is balanced when P/Q = R/S. In balanced condition, potential difference across galvanometer is zero, hence no current flows through it.
Q.74Easy
Which of the following materials has the highest temperature coefficient of resistance?
Answer: B
Tungsten has the highest temperature coefficient (≈0.0045/°C) among metals, making it suitable for filament bulbs.
Q.75Medium
A cell of EMF E and internal resistance r is connected to an external resistance R. The terminal voltage V is given by:
Answer: C
Terminal voltage V = E - Ir, where I is the current through the circuit. The voltage drop occurs only across internal resistance.
Q.76Medium
A potentiometer wire of length 100 cm has resistance 10Ω. A standard cell of EMF 1.5V is balanced at 60 cm. What is the EMF of unknown cell if it balances at 80 cm?
The resistivity of a semiconductor at absolute zero is:
Answer: B
At absolute zero, there are no free charge carriers in a semiconductor, making its resistivity infinite.
Q.78Medium
A nichrome wire and a copper wire of same length and area are connected in series. Which experiences greater heat dissipation?
Answer: A
Heat dissipated H = I²Rt. Since same current flows through both and nichrome has higher resistivity than copper (higher R), nichrome dissipates more heat.
Q.79Medium
In a meter bridge experiment, the null point is obtained at 40 cm from the left end. If the left resistance is 8Ω, what is the right resistance?
Answer: A
In meter bridge: R₁/R₂ = l₁/(100-l₁). So 8/R₂ = 6040, giving R₂ = 12Ω
Q.80Easy
The current density in a conductor depends on:
Answer: C
Current density J = σE = neE, where σ is conductivity. It depends on both electric field and material properties (conductivity).
