A light bulb rated 60W, 120V is connected to a 120V supply. The resistance of the bulb is:
R = V²/P = (120)²/60 = 6014400 = 240Ω
Three identical cells, each of EMF 1.5V and internal resistance 1Ω, are connected in series. The total EMF and internal resistance are:
In series: Total EMF = 1.5 + 1.5 + 1.5 = 4.5V. Total internal resistance = 1 + 1 + 1 = 3Ω
A rheostat is used in a circuit to:
A rheostat is a variable resistor used to control and vary the current in a circuit
In a parallel combination of resistors, the voltage across each resistor is:
In parallel combination, all resistors are connected across same two points, hence voltage across each is same
In a circuit with a battery of 10V and total resistance 5Ω, the power dissipated is:
P = V²/R = (10)²/5 = 5100 = 20W
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In a circuit, if the current increases when voltage increases, the resistance must:
From Ohm's law: I = V/R. If I increases with increasing V while R stays constant, then the relationship is proportional and follows Ohm's law
Which of the following materials has the lowest temperature coefficient of resistance?
Constantan (copper-nickel alloy) has the lowest temperature coefficient of resistance, making it ideal for standard resistors
In a Wheatstone bridge, if P/Q = R/S, then the galvanometer shows zero deflection. This condition is called:
Both balance condition and null point refer to the same situation where no current flows through the galvanometer
Five resistors each of 5Ω are connected in parallel. The equivalent resistance is:
For parallel: 1/R_eq = 5×(51) = 1, so R_eq = 1Ω
The specific resistance (resistivity) of a material depends on:
Resistivity is an intrinsic property dependent on the material's nature and temperature, not on the dimensions or electrical parameters
The drift velocity of electrons in a conductor is of the order of:
Drift velocity is typically 10⁻⁴ to 10⁻³ m/s, much smaller than electron thermal velocity or speed of electrical signal
The resistance of a wire at 0°C is R₀. If its temperature coefficient is α, its resistance at temperature T is:
R_T = R₀(1 + αT), where T is temperature rise from reference point (0°C in this case)
Two resistances of 3Ω and 6Ω are connected in parallel. The equivalent resistance is:
For parallel: 1/Rₑq = 31 + 61 = 63 = 21, so Rₑq = 2Ω
Which of the following materials has the highest temperature coefficient of resistance?
Tungsten has the highest temperature coefficient (≈0.0045/°C) among metals, making it suitable for filament bulbs.
The resistivity of a semiconductor at absolute zero is:
At absolute zero, there are no free charge carriers in a semiconductor, making its resistivity infinite.
The current density in a conductor depends on:
Current density J = σE = neE, where σ is conductivity. It depends on both electric field and material properties (conductivity).
A copper wire at 20°C has resistance 100Ω. Its resistance at 120°C is (α for copper = 0.004/°C):
R = R₀[1 + α(T-T₀)] = 100[1 + 0.004(120-20)] = 100[1 + 0.4] = 140Ω
In a carbon resistor, the color bands are Brown-Black-Red-Gold. Its resistance is:
Brown=1, Black=0, Red=2 (multiplier=10²=100), Gold=5% tolerance. Resistance = 10×100 = 1000Ω ± 5%
