Electricity — Set 2
Physics · विद्युत · Questions 11–20 of 60
The SI unit of electric field is?
Correct Answer: C. N/C
Electric field is force per unit charge. So its unit can be written as newton per coulomb (N/C). It can also be expressed as volt per meter (V/m).
According to Coulomb’s law, the electrostatic force between two point charges is proportional to?
Correct Answer: D. r
Coulomb’s law states that force varies inversely with the square of distance. It is written as F ∝ 1/r^2 for fixed charges. The force also depends on the product of the charges.
Two charges 2 μC and 3 μC are 0.5 m apart in vacuum. What is the force between them? (k = 9×10^9 N m^2/C^2)?
Correct Answer: C. 2.16 N
Use F = k q1 q2 / r^2. Substituting q1 = 2×10^-6, q2 = 3×10^-6, r = 0.5 gives F = 9×10^9×6×10^-12/0.25 = 0.216 N. Like charges repel and unlike charges attract.
Potential difference between two points is defined as?
Correct Answer: A. Work done per unit charge
Potential difference is the work done per unit charge to move a test charge. It is written as V = W/Q. Its SI unit is volt (V).
If 20 J of work is done to move 5 C of charge, what is the potential difference?
Correct Answer: B. 25 V
Use V = W/Q. Substituting W = 20 J and Q = 5 C gives V = 20/5 = 4 V. Voltage is also called electric potential difference.
Electromotive force (emf) of a source is best described as?
Correct Answer: B. Resistance of the source
EMF is the energy supplied by a source per unit charge. It is measured in volt like potential difference. EMF is the open-circuit voltage when no current is drawn.
In a metallic conductor, the direction of conventional current is?
Correct Answer: D. Same as electron drift
Conventional current is defined as the flow of positive charge. In metals, electrons move opposite to this direction. Therefore conventional current is opposite to electron drift.
A 5 Ω resistor carries 2 A current. What power is dissipated in it?
Correct Answer: D. 5 W
Use P = I^2R. Substituting I = 2 A and R = 5 Ω gives P = 4×5 = 20 W. Electrical energy is converted to heat in a resistor.
A fuse is connected in?
Correct Answer: C. Series with the appliance in the neutral wire only
A fuse must stop current to protect the circuit. It is connected in series so that it can break the circuit when current exceeds a limit. It is generally placed in the live wire for safety.
Heat produced in a resistor R when current I flows for time t is?
Correct Answer: C. H = I^2Rt
Joule’s law of heating gives H = I^2Rt. It shows heating increases with the square of current. This principle is used in electric heaters and fuses.