A light bulb rated 60W, 120V is connected to a 120V supply. The resistance of the bulb is:
A 120Ω B 240Ω C 60Ω D 180Ω
R = V²/P = (120)²/60 = 60 14400
Three identical cells, each of EMF 1.5V and internal resistance 1Ω, are connected in series. The total EMF and internal resistance are:
A 4.5V, 1Ω B 1.5V, 3Ω C 4.5V, 3Ω D 3V, 3Ω
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 Measure current B Vary the current in the circuit C Measure voltage D Detect current direction
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:
A Different for each resistor B The same for all resistors C Sum of individual voltages D Proportional to resistance values
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:
A 50W B 25W C 20W D 2W
P = V²/R = (10)²/5 = 5 100
In a circuit, if the current increases when voltage increases, the resistance must:
A Increase B Decrease C Remain constant D Become zero
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?
A Copper B Constantan C Nichrome D Aluminum
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:
A Balance condition B Null point C Both A and B D Neither A nor B
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:
A 25Ω B 5Ω C 1Ω D 0.2Ω
For parallel: 1/R_eq = 5×(5 1
The specific resistance (resistivity) of a material depends on:
A Length and cross-sectional area only B Temperature and nature of material only C Current flowing through it D Voltage applied across it
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:
A 10⁸ m/s B 10⁻⁴ m/s C 10⁻² m/s D 10³ m/s
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:
A R₀(1 + αT) B R₀αT C R₀/(1 + αT) D R₀(1 - αT)
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:
A 2Ω B 9Ω C 4.5Ω D 18Ω
For parallel: 1/Rₑq = 3 1 6 1 6 3 2 1
Which of the following materials has the highest temperature coefficient of resistance?
A Copper B Tungsten C Constantan D Nichrome
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:
A Zero B Infinite C Same as at room temperature D Undefined
At absolute zero, there are no free charge carriers in a semiconductor, making its resistivity infinite.
The current density in a conductor depends on:
A Only electric field B Only charge carrier density C Electric field and properties of conductor D Temperature only
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):
A 140Ω B 120Ω C 160Ω D 180Ω
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:
A 1000Ω ± 5% B 1200Ω ± 5% C 2000Ω ± 5% D 1000Ω ± 10%
Brown=1, Black=0, Red=2 (multiplier=10²=100), Gold=5% tolerance. Resistance = 10×100 = 1000Ω ± 5%
A charged particle moves in a uniform magnetic field perpendicular to its velocity. Which of the following remains constant?
A Kinetic energy of the particle B Magnetic force on the particle C Radius of circular path D Angular velocity of the particle
When a charged particle moves perpendicular to a uniform magnetic field, the magnetic force is always perpendicular to velocity, so it does no work. Hence kinetic energy remains constant. However, direction changes continuously.
The magnetic field at the center of a circular loop of radius R carrying current I is:
A μ₀I/2R B μ₀I/4πR C μ₀I/2πR D μ₀I/πR
Using Biot-Savart law, the magnetic field at the center of a circular loop of radius R carrying current I is B = μ₀I/2R. This is a fundamental formula in magnetism.
