Electric Charges and Fields — Physics STD 12 Science — Question

The adjoining figure shows a negatively charged electroscope. If a negatively charged rod is brought close to, but not touching, the knob, the two leaves will:

A current of 10A is passing through a long wire which has semicircular loop of the radius 20cm as shown in the figure. Magnetic field produced at the centre of the loop is

(a) 10 πμT

(b) 5 πμT

(c) 4 πμT

(d) 2 πμT

A circular coil of radius R carries an electric current. The magnetic field due to the coil at a point on the axis of the coil located at a distance r from the centre of the coil, such that r >> R, varies as

(a)

(b)

(c)

(d)

The dielectric strength of air at NTP is 3  then the maximum charge that can be given to a spherical conductor of radius 3 m is

(a) 3

(b) 3

(c) 3

(d) 3

The focal length of the objective lens of a compound microscope is

(a) Equal to the focal length of its eye piece

(b) Less than the focal length of eye piece

(c) Greater than the focal length of eye piece

(d) Any of the above three

The magnetic moment (μ) of a revolving electron around the nucleus varies with principal quantum number n as

(a) μ ∝ n

(b) μ ∝ 1/n

(c) μ ∝

(d) μ ∝ 1/

The current through choke coil increases form zero to 6A in 0.3 seconds and an induced e.m.f. of 30 V is produced. The inductance of the coil of choke is

(a) 5 H

(b) 2.5 H

(c) 1.5 H

(d) 2 H

200 MeV of energy may be obtained per fission of . A reactor is generating 1000 kW of power. The rate of nuclear fission in the reactor is

(a) 1000

(b) 2

(c) 3.125

(d)  931

Which gates is represented by this figure

(a) NAND gate

(b) AND gate

(c) NOT gate

(d) OR gate

There are two charges +1 microcoulombs and +5 microcoulombs. The ratio of the forces acting on them will be

(a) 1 : 5

(b) 1 : 1

(c) 5 : 1

(d) 1 : 25