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

The ratio of areas within the electron orbits for the first excited state to the ground state for hydrogen atom is

(a) 16 : 1

(b) 18 : 1

(c) 4 : 1

(d) 2 : 1

The mutual inductance of an induction coil is 5H. In the primary coil, the current reduces from 5A to zero in  . What is the induced emf in the secondary coil

(a) 2500 V

(b) 25000V

(c) 2510V

(d) Zero

There is a relation between the radius (R) of the nucleus of an atom and the mass number (A) of the atom :

Which of the following is not reversible

(a) Joule effect

(b) Peltier effect

(c) Seebeck effect

(d) Thomson effect

Which of the following is NOT a postulate of Bohr's model of the hydrogen atom? 

When a magnet is pushed in and out of a circular coil C connected to a very sensitive galvanometer G as shown in the adjoining diagram with a frequency v, then

(a) Constant deflection is observed in the galvanometer

(b) Visible small oscillations will be observed in the galvanometer if v is about 50 Hz

(c) Oscillations in the deflection will be observed clearly if v = 1 or 2 Hz

(d) No variation in the deflection will be seen if v = 1 or 2 Hz

Assertion  :   A parallel plate capacitor is connected across battery through a key. A dielectric slab of constant K is introduced between the plates. The energy which is stored becomes K times.

Reason     : The surface density of charge on the plate remains constant or unchanged.

(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 retarding potential for having zero photo-electron current

(a) Is proportional to the wavelength of incident light

(b) Increases uniformly with the increase in the wavelength of incident light

(c) Is proportional to the frequency of incident light

(d) Increases uniformly with the increase in the frequency of incident light wave

The work function of a metallic surface is 5.01 eV. The photo-electrons are emitted when light of wavelength 2000Å falls on it. The potential difference applied to stop the fastest photo-electrons is  [h = 4.14

(a) 1.2 volts

(b) 2.24 volts

(c) 3.6 volts

(d) 4.8 volts

When the intensity of light falling on a surface producing photoelectric effect is doubled, then :