Current Electricity — Physics STD 12 Science — Question

A radioactive sample at any instant has its disintegration rate 5000 disintegration per minute. After 5 minutes, the rate is 1250 disintegrations per minute. Then, the decay constant (per minute) is

(a) 0.8 In 2

(b) 0.4 In 2

(c) 0.2 In 2

(d) 0.1 In 2

A P-type semiconductor has acceptor levels 57 meV above the valence band. The maximum wavelength of light required to create a hole is (Planck’s constant h = 6.6  J-s)

(a) 57

(b) 57

(c) 217100

(d) 11.61

According to Lenz's law there is conversion of:

When charged particle enters-a uniform magnetic field, its K.E:

What is the net force on the square coil

(a) 25  moving towards wire	(b) 25  moving away from wire
(c) 35   moving towards wire	(d) 35   moving away from wire

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.

A transformer has 100 turns in the primary coil and carries 8 A current. If input power is one kilowatt, the number of turns required in the secondary coil to have 500V output will be

(a) 100

(b) 200

(c) 400

(d) 300

The drift current in a p-ri junction is:

A cube of side b  has a charge q at each of its vertices. The electric field due to this charge distribution at the centre of this cube will be

(a)

(b)

(c)

(d) Zero