Physics Questions & Answers - Free Online Practice

1,366.

Lenz's law is a law of conservation of

electric charge

electric current

Energy

Momentum

View answer & explanation

Correct answer is C

Lenz's lew of electrical magnetic induction is usefully referred to as the law of conservation of energy

1,367.

Two long parallel wires X and Y carry currents 3A and 5A each. if the force experienced by unit length is 5 x 10^-5N. the force per unit length experienced by wire Y is

3 x 10^-5

3 x 10^-6

5 x 10⁵

5 x 10^-5

View answer & explanation

Correct answer is D

since the wires are parallel to each other, the forces which they exert on each other are equal and opposite, since they must agree with newton's law of action an reaction. Hence the force exerted by the wire is equally
5 x 10^-5

1,368.

The instrument that measures both ac and dc is called

A current balance

a moving coil ammeter

a moving iron ammeter

an inverter

View answer & explanation

Correct answer is C

No explanation has been provided for this answer.

1,369.

A 40KW electric cable was uses to transmit electricity through a resistor of resistance 2.00Ω at 800V. The power loss as internal energy is

4.0 x 10²W

5.0 x 10²W

4.0 x 10³W

5.0 x 10³W

View answer & explanation

Correct answer is D

In general, Power = IV; $\implies 40KW = IV \\ \text{Therefore } 40000 = 1 \times 800\\ \implies I = \frac{40000}{800} = 50A,\text{tune the current through}$

Resistor = 50A
power loss= I²R = 50² x 2
= 2500 x 2 = 5.0 x 10³W

1,370.

A conductor has a diameter of 1.00mm and length of 2.00m. If the resistance of the material is 0.1Ω, the resistivity is

2.55 * 10⁵ Ωm

2.55 * 10³ Ωm

3.93 * 10^-6 Ωm

3.93 * 10^-8 Ωm

View answer & explanation

Correct answer is D

$R = \frac{1}{a} p \implies p = \frac{R.a}{1} = \frac{0.1 \times 3.14}{2} \left ( \frac{10^{-3}}{2} \right)^2 \\ \text{Therefore } p = \frac{0.1 \times 3.14 \times 10^{-6}}{2 \times 4} \\ = 0.3925 \times 10^{-7} \text{ OR } -3.930 \times 10 ^{-8}Ωm$