Magnetism And Matter — Physics STD 12 Science — Question

The self inductance L of a solenoid of length l and area of crosssection A, with a fixed number of turns N increases as:

Near and far points of a human eye are

(a) 0 and 25 cm

(b) 0 and ¥

(c) 25 cm and 100 cm

(d) 25 cm and ¥

Assertion :   The force with which one plate of a parallel plate capacitor is attracted towards the other plate is equal to square of surface density per e per unit area.

Reason     : The electric field due to one charged plate of the capacitor at the location of the other is equal to surface density per e.

(a) If both assertion and reason are true and the reason is the correct explanation of the assertion.

(b) If both assertion and reason are true but reason is not the correct explanation of the assertion.

(c) If assertion is true but reason is false.

(d) If the assertion and reason both are false.

The incident photon involved in the photoelectric effect experiment.

(a) Completely disappears

(b) Comes out with an increased frequency

(c) Comes out with a decreased frequency

(d) Comes out without change in frequency

The minimum wavelength of photon is 5000 Å, its energy will be

(a) 2.5 eV

(b) 50 V

(c) 5.48 eV

(d) 7.48 eV

The focal lengths of the objective and eye-lens of a microscope are 1 cm and 5 cm respectively. If the magnifying power for the relaxed eye is 45, then the length  of the tube is

(a)  30 cm

(b)  25 cm

(c)  15 cm

(d)  12 cm

The coil of dynamo is rotating in a magnetic field. The developed induced e.m.f. changes and the number of magnetic lines of force also changes. Which of the following condition is correct

(a) Lines of force minimum but induced e.m.f. is zero

(b) Lines of force maximum but induced e.m.f. is zero

(c) Lines of force maximum but induced e.m.f. is not zero

(d) Lines of force maximum but induced e.m.f. is also maximum

Bell laboratory has developed superconductor at a temperature of:

Which of the following statement is false:

The number of electrons to be put on a spherical conductor of radius 0.1m to produce an electric field of 0.036 N/C  just above its surface is

(a) 2.7

(b) 2.6

(c) 2.5

(d) 2.4