A thin wire of resistance 4Ω is bent to form a circle. The resistance across any diameter is

• 4 Ω

• 2 Ω

• 1 Ω

• 8 Ω

A battery of e.m.f. E and internal resistance r is connected to an external resistance R the condition for maximum power transfer is

• r < R

• r > R

• r = 1/R

• r = R

Two wires each of same material and same length have 2 : 1 ratio of their radii. If the first wire has a resistance of 2 Ω then what will be the equivalent resistance of the two wires when they are connected in series ?

What should be the resistance of an ideal ammeter and an ideal voltmeter ?

A 60 W- 220 V bulb is connected in series with another bulb 40 W-220 V. Which bulb will give more illuminance ?

A wire of length 5 m is stretched by 1 mm by a force of 1 N. What is the value of energy stored in the wire ?

One kg of copper is drawn into a wire of 1 mm diameter and a wire of 2 mm diameter. The resistance of the two wires will be in the ratio

• 2 : 1

• 1 : 2

• 16 : 1

• 4 : 1

418.

An electrical cable having a resistance of 0.2 Ω delivers 10 kW at 200 V DC to a factory. What is the efficiency of transmission ?

• 65 %

• 75 %

• 85 %

• 95 %

A wire of resistance 5 Ω is drawn out so that its new length is 3 times its original length. What is the resistance of the new wire ?

• 45 Ω

• 15 Ω

• 5/3 Ω

• 5 Ω

Two identical cells each of emf E and internal resistance r are connected in parallel with an external resistance R. To get maximum power developed across R, the value of R is

• $\mathrm{R} = \frac{\mathrm{r}}{2}$

• R = r

• $\mathrm{R} = \frac{\mathrm{r}}{3}$

• R = 2r