Ray Optics and Optical Instruments — Physics STD 12 Science — Question

A parallel plate capacitor is connected to a battery as shown in Fig. Consider two situations:
A: Key K is kept closed and plates of capacitors are moved apart using insulating handle.
B: Key K is opened and plates of capacitors are moved apart using insulating handle. Choose the correct option(s).

Light takes 8 min 20 sec to reach from sun on the earth. If the whole atmosphere is filled with water, the light will take the time    (a

(a) 8 min 20 sec

(b) 8 min

(c) 6 min 11 sec

(d) 11 min 6 sec

In a photo-diode, 

Electric charges of +10μC, + 5μC, -3μC and +8 μC  are placed at the corners of a square of side  m. the potential at the centre of the square is

(a) 1.8 V

(b)  V

(c) 1.8

(d) 1.8  V

A straight wire of diameter 0.5 mm carrying a current of 1 A is replaced by another wire of 1 mm diameter carrying the same current. The strength of magnetic field far away is

(a) Twice the earlier value	(b) Half of the earlier value
(c) Quarter of its earlier value	(d) Unchanged

The field lines of a single positive charge are:

Assertion  :   Silicon is preferred over germanium for making semiconductor devices.

Reason      : The energy gap for germanium is more than the energy gap of silicon.

(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.

Which of the following is based on mechanical effect of electric current?