Atoms — Physics STD 12 Science — Question

To get the maximum current from a parallel combination of n identical cells each of internal resistance r in an external resistance R, when

(a) R >> r

(b) R << r

(c) R = r

(d) None of these

16 gm sample of a radioactive element is taken from Bombay to Delhi in 2 hour and it was found that 1 gm of the element remained (undisintegrated). Half life of the element is

(a) 2 hour

(b) 1 hour

(c)

(d)

A copper wire has a square cross-section, 2.0 mm on a side.  It carries a current of 8 A and the density of free electrons is 8  . The drift speed of electrons is equal to

(a) 0.156 ×   m.s–1

(b) 0.156 ×   m.s–1

(c) 3.12 ×   m.s–1

(d) 3.12 ×   m.s–1

Which of the following particles are constituents of the nucleus

(a) Protons and electrons	(b) Protons and neutrons
(c) Neutrons and electrons	(d) Neutrons and positrons

An electric dipole has a pair of equal and opposite point charges q and –q separated by a distance 2x. The axis of the dipole is:

Two identical cycle wheels (geometrically) have different number of spokes connected from center to rim. One is having 20 spokes and the other having only 10 (the rim and the spokes are resistanceless). One resistance of value R is connected between center and rim. The current in R will be.

Force between two unit pole strength placed at a distance of one metre is

(a) 1 N

(b)

(c)

(d) 4π

By ammeter, which of the following can be measured

(a) Electric potential

(b) Potential difference

(c) Current

(d) Resistance

Two charged particles traverse identical helical paths in a completely opposite sense in a uniform magnetic field.

In the shown arrangement of the experiment of the meter bridge if AC corresponding to null deflection of galvanometer is x, what would be its value if the radius of the wire AB is doubled

(a) x

(b) x/4

(c) 4x

(d) 2x