Nucleus — Physics STD 12 Science — Question

A very thin film in reflected white light appears:

If 20 gm of a radioactive substance due to radioactive decay reduces to 10 gm in  4 minutes, then in what time 80 gm of the same substance will reduce to 10 gm

(a) In 8 minutes

(b) In 12 minutes

(c) In 16 minutes

(d) In 20 minutes

In the circuit shown in figure, the current drawn from the battery is 4A.  If 10 W resistor is replaced by 20 W resistor, then current drawn from the circuit will be

(a) 1 A

(b) 2 A

(c) 3 A

(d) 0 A

Constantan wire is used in making standard resistances because its

(a) Specific resistance is low

(b) Density is high

(c) Temperature coefficient of resistance is negligible

(d) Melting point is high

The Sun's mean density is:

The potential drop across the 3W resistor is

(a) 1 V

(b) 1.5 V

(c) 2 V

(d) 3 V

Assertion   : The following circuit represents 'OR' gate

Reason     : For the above circuit Y =

(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.

Two infinitely long parallel conducting plates having surface charge densities +σ and -σ respectively, are separated by a small distance. The medium between the plates is vacuum. If  is the dielectric permittivity of vacuum, then the electric field in the region between the plates is

(a) 0 volts/meter

(b)  volts/meter

(c)  volts/meter

(d)  volts/meter

According to Planck’s quantum theory any electromagnetic radiation is: