Dual Nature of Radiation and Matter

Monochromatic light of frequency 6 1014 Hz is produced by a laser. The power emitted is 2 10-3 W. How many photons per second on an average, are emitted by the source ? (Given h=6.63 10-34 Js)

1. 5 1015
2. 7 1016
3. 6 1015
4. 9 1018

When a metal surface is illuminated by light of wavelength , the stopping potential is 8 V. When the same surface is illuminated by light of wavelength 3 , stopping potential is 2 V. The threshold wavelength for this surface is:

1. 3
2. 9
3. 5
4. 4.5

In a photoelectric effect experiment a light of frequency 1.5 times the threshold frequency is made to fall on the surface of photosensitive material. Now if the frequency is halved and intensity is doubled, the number of photo electrons emitted will be:

1. doubled
2. halved
3. Zero
4. quadrupled

The work function of a substance is 3.0 eV. The longest wavelength of light that can cause the emission of photoelectrons from this substance is approximately;

1. 215 nm
2. 400 nm
3. 414 nm
4. 200 nm

For the photoelectric effect, the maximum kinetic energy (Ek) of the photoelectrons is plotted against the frequency ( ) of the incident photons as shown in figure. The slope of the graph gives [figure]

1. Planck's constant
2. Work function of the metal
3. Charge of electron
4. Ratio of Planck's constant to electric charge

The de-Broglie wavelength of an electron is the same as that of a photon. If velocity of electron is 25\% of the velocity of light, then the ratio of K.E. of electron and K.E. of photon will be:

1. 14
2. 81
3. 18
4. 11

Two sources of light emit with a power of 200 W. The ratio of number of photons of visible light emitted by each source having wavelengths 300 nm and 500 nm respectively, will be :

1. 5:3
2. 3:5
3. 1:5
4. 1:3

A convex lens of focal length 40 cm forms an image of an extended source of light on a photoelectric cell. A current I is produced. The lens is replaced by another convex lens having the same diameter but focal length 20 cm. The photoelectric current now is :

1. I2
2. 4 I
3. 2 I
4. I

The threshold frequency of a metal with work function 6.63 eV is :

1. 16 1015 Hz
2. 16 1012 Hz
3. 1.6 1015 Hz
4. 1.6 1012 Hz