Physics is where JEE ranks are usually won or lost, since a single conceptual slip changes the whole answer. Questions here span mechanics, rotational motion, thermodynamics, waves and oscillations, electrostatics, current electricity, magnetism, optics, and modern physics. Numerical problems carry full derivations so you can see which step you skipped, not just which option was right.
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.
