A battery of EMF E and internal resistance r is connected to an external resistance R. The terminal voltage is:
Answer: D
Terminal voltage V = E - Ir. Since I = E/(R+r), we get V = E - Er/(R+r) = ER/(R+r). Both expressions are equivalent
Q.22Easy
In carbon resistors, color bands are used for identification. What does the third band represent?
Answer: C
Standard color code: 1st band = first digit, 2nd band = second digit, 3rd band = multiplier, 4th band = tolerance
Q.23Easy
The internal resistance of a Leclanche cell is approximately:
Answer: B
Standard Leclanche cells have internal resistance in the range of 1-2Ω depending on size and condition
Q.24Medium
In a potentiometer, if the balancing length for a cell is 60 cm and for standard cell is 50 cm, what is the EMF of the unknown cell? (Standard cell = 1.018V)
Answer: B
E/E_std = L/L_std, so E = 1.018 × (5060) = 1.018 × 1.2 = 1.2216 ≈ 1.221 V
Q.25Easy
An electric heater rated 500W, 250V is used for 4 hours daily. The energy consumed in one day is:
Answer: A
Energy = Power × Time = 500W × 4h = 2000Wh = 2 kWh
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Q.26Hard
The equivalent resistance between two opposite corners of a cube made of 12 wires of 1Ω each is:
Answer: B
Due to symmetry, current divides into three paths of 1Ω each in parallel at the first vertex, then similar distribution at other vertices. Equivalent = 31 + 61 + 31 = 65Ω
Q.27Easy
If the cross-sectional area of a wire is doubled while keeping length and material constant, how does resistivity change?
Answer: C
Resistivity is a material property independent of shape and size. It depends only on the nature of material and temperature
Q.28Easy
The temperature coefficient of resistance for a conductor is positive. This means:
Answer: A
Positive temperature coefficient means R = R₀(1 + αΔT) where α > 0, so resistance increases with increasing temperature
Q.29Medium
A galvanometer with coil resistance 100Ω shows full-scale deflection at 10 mA. What shunt resistance is needed to convert it into an ammeter reading up to 1 A?
In a circuit with pure resistance, the phase difference between voltage and current is:
Answer: A
In a purely resistive circuit, voltage and current are in phase, so phase difference is 0°. V = IR is always satisfied
Q.31Medium
A rectangular conductor with dimensions 2cm × 3cm × 10cm is placed such that current flows through the 10cm length. If resistivity is 1.7 × 10⁻⁸ Ω·m, find the resistance:
A copper wire of length L and cross-sectional area A has resistance R. If the wire is stretched to double its length while maintaining the same volume, what is the new resistance?
Answer: B
When stretched to double length, volume remains constant. New area = A/2. R' = ρL'/A' = ρ(2L)/(A/2) = 4ρL/A = 4R
Q.33Easy
In a circuit, three resistors of 2Ω, 3Ω, and 6Ω are connected in parallel. The equivalent resistance is:
