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.362Medium
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.363Easy
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.364Medium
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.365Medium
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.367Medium
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.368Medium
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.369Easy
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).
Q.370Medium
A battery of EMF 10V supplies current to a circuit. If the voltage across external resistance is 9V, what is the internal resistance if external resistance is 90Ω?
Answer: B
V = E - Ir. 9 = 10 - I×r. Current I = V/R = 909 = 0.1A. So 9 = 10 - 0.1r, giving r = 10Ω
Q.371Medium
In a circuit with capacitors, which quantity is continuous across the capacitor?
Answer: C
In DC circuits, current is continuous (same) through all series elements including capacitors in steady state. However, in AC circuits, current flows through capacitors.
Q.372Hard
The length of a conductor increases by 10% when stretched. Assuming volume remains constant, the resistance increases by approximately:
Answer: C
R = ρL/A. If L increases by 10% and volume constant, A decreases by ~9.1%. New R = 1.1R₀/0.91 ≈ 1.21R₀, so 21% increase.
Q.373Hard
The equivalent resistance of an infinite ladder network of 1Ω resistors (each rung) is:
Tungsten filament's resistance increases significantly with temperature due to heating, causing non-linear I-V characteristic (non-ohmic).
Q.377Medium
In Joule heating, if voltage is doubled and resistance is halved, the power dissipated becomes:
Answer: C
P = V²/R. New P = (2V)²/(R/2) = 4V²×2/R = 8(V²/R) = 8P₀
Q.378Hard
A superconductor exhibits zero resistance below its critical temperature because:
Answer: B
BCS theory explains superconductivity: below critical temperature, electrons form Cooper pairs with no scattering, resulting in zero resistance.
Q.379Medium
A wire of length L and cross-sectional area A has resistance R. If the wire is stretched to 1.5 times its original length without change in volume, what will be its new resistance?
Answer: A
When stretched, length becomes 1.5L. Volume remains constant (LA = A'L'), so A' = A/1.5. New resistance R' = ρ(1.5L)/(A/1.5) = 2.25ρL/A = 2.25R
Q.380Medium
A heating element rated 1000W, 220V is connected to a 110V supply. The heat produced becomes:
Answer: A
Resistance of element R = V²/P = 220²/1000 = 48.4Ω (constant). At 110V: P' = V'²/R = 110²/48.4 ≈ 250W. Power varies with square of voltage.
