In the Wheatstone's network given, P = 10Ω, Q = 20Ω, R =15Ω, S = 30Ω, the current passing through the battery (of negligible internal resistance) is

• 0.36 A

• zero

• 0.18 A

• 0.72 A

A wire of length L has resistance R. It is bent at mid-point such that the two halves make an angle 90° with each other. The new resistance would be.

• R

• $\sqrt{2}$ R

• $\frac{\mathrm{R}}{\sqrt{2}}$

• $\frac{R}{4}$

N identical cells, each of emf E, are connected in parallel. The emf of the combination is

• NE

• E

• N²E

• E/N

Therm-ions are

• photons

• protons

• electrons

• nuclei

Kirchhoff's law of junction, $\mathrm{\Sigma }$I = 0, is based on :

• conservation of energy

• conservation of charge

• conservation of energy as well as charge

• conservation of momentum

136.

If the percentage change in current through a resistor is 1%, then the change in power through it would be:

• 1 %

• 2 %

• 1.7 %

• 0.5 %

3 identical bulbs are connected in series and these together dissipate a power P. If now the bulbs are connected in parallel, then the power dissipated will be:

• P/3

• 3P

• 9P

• P/9

What is the drift velocity of electrons if the current flowing through a copper wire of 1 mm diameter is 1.1 A. Assume that each atom of copper contributes one electron : (Given: density of Cu = 9 g/cm³ and atomic weight of Cu = 63)

• 0.3 mm/s

• 0.5 mm/s

• 0.1 mm/s

• 0.2 mm/s

The equivalent resistance between A and B is

• 10 Ω

• 20 Ω

• 30 Ω

• 49 Ω

An electrical cable of copper has just one wire of radius 9 mm. Its resistance is 5Ω. The single wire of the cable is replaced by 6 different well-insulated copper wires each of radius 3 mm. The total resistance of the cable will now be equal to:

• 270 Ω

• 90 Ω

• 45 Ω

• 7.5 Ω