Moving Charges and Magnetism — Physics STD 12 Science — Question

The capacitance of an air capacitor is 15 μF the separation between the parallel plates is 6mm. A copper plate of 3mm  thickness is introduced symmetrically between the plates.  The capacitance now becomes

(a) 5 μF

(b) 7.5 μF

(c) 22.5 μF

(d) 30 μF

Light from a hydrogen discharge tube is incident on the cathode of a photoelectric cell the work function of the cathode surface is 4.2 eV. In order to reduce the photo-current to zero the voltage of the anode relative to the cathode must be made

(a) – 4.2 V

(b) – 9.4 V

(c) – 17.8 V

(d) +9.4 V

The heating coils rating at 220 volt and producing 50 cal/sec heat are available with the resistances 55Ω,110 Ω, 220 Ω   and 440 Ω. The heater of maximum power will be of

(a) 440 Ω

(b) 220 Ω

(c) 110 Ω

(d) 55 Ω

Which of the following is true for number of spectral lines in going form Layman series to Pfund series

(a) Increases	(b) Decreases
(c) Unchanged	(d) May decreases or increases

A charged particle is moving with velocity v in a magnetic field of induction B. The force on the particle will be maximum when

(a) v and B are in the same direction	(b) v and B are in opposite directions
(c) v and B are perpendicular	(d) v and B are at an angle of 45°

A circular loop is kept in that vertical plane which contains the north-south direction. It carries a current that is towards north at the topmost point. Let A be a point on the axis of the circle to the east of it and B a point on this axis to the west of it. The magnetic field due to the loop

Can a metal be used as a medium for dielectric

(a) Yes

(b) No

(c) Depends on its shape

(d) Depends on dielectric

The minimum heat energy required to emit an electron from the surface of a metal is called _________:

According to modern astronomers into how many constellations, the whole sky is divided

(a) 1011

(b) 88

(c) 880

(d) 5000

The minimum temperature of a body at which it emits light is

(a) 1200°C

(b) 1000°C

(c) 500°C

(d) 200°C