Electric Charges and Fields — Physics STD 12 Science — Question

If  and  are respectively the filament resistances of a 200 watt bulb and 100 watt bulb designed to operate on the same voltage, then

(a)  is two times	(b)  is two times
(c)  is four times	(d)  is four times

The electrical conductivity of semiconductor increases when electromagnetic radiation of wavelength shorter than 2800 nm is incident on it. The band gap in (eV) for the semiconductor is:

In the given circuit, if A and B represent two inputs and C represents the output, the circuit represents:

We have two wires A and B of same mass and same material.  The diameter of the wire A is half of that B.  If the resistance of wire A is 24 ohm then the resistance of wire B will be

(a) 12 Ohm

(b) 3.0 Ohm

(c) 1.5 Ohm

(d) None of the above

Assertion : The resistivity of a semiconductor increases with temperature.

Reason     : The atoms of a semiconductor vibrate with larger amplitude at higher temperature there by increasing it's resistivity.

(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.

Conservation of electric charges means that the total charge of an isolated system remains ____ with time.

The eye can detect 5 × 10⁴ photons per square metre per sec of green light (l = 5000 Å) while the ear can detect  . The factor by which the eye is more sensitive as a power detector than the ear is close to

(a) 5

(b) 10

(c) 106

(d) 15

Time taken by the sunlight to pass through a window of thickness 4 mm whose refractive index is 1.5 is

(a) 2  sec

(b) 2 sec

(c) 2  sec

(d) 2   sec

If   and   are the electric and magnetic field vectors of E.M. waves then the direction of propagation of E.M. wave is along the direction of

(a)

(b)

(c)

(d) None of these