dawn of modern physics

Question 1

Black-Body Radiations

Answer 1

The radiations emitted from a hollow black coated having small hole due to temperature are called black body radiations. The wave length of such radiations decreases with the increase of temperature.

Blackbody radiation refers to the spectrum of light emitted by any heated object; common examples include the heating element of a toaster and the filament of a light bulb

Question 2

Ideal/ Perfect Black Body

Answer 2

A body which absorbs all the radiations incident upon it is called an ideal/perfect black body.
Example:
When platinum wire is heated, it appears dull red at 500°C, cherry red at 900°C Orange red at 1100°C, yellow at 1300°C White at 1600°C.

Question 3

Photo-electric Effect

Answer 3

When the light of a suitable frequency is incident on metal surface, the electrons are emitted from surface which are called photo electrons and this process is called photoelectric effect.

Question 4

Photo-electric Current

Answer 4

The current produced by these photo electrons is called photoelectric current.

Question 5

Stopping potential

Answer 5

The negative potential of anode at which photoelectric current becomes zero is called stopping potential. Photoelectric current increase with intensity of light

Question 6

Threshold frequency

Answer 6

The minimum value of frequency of incident light at which electrons are emitted from a metal surface is called threshold frequency

Question 7

Work Function

Answer 7

The minimum energy required to escape the electrons from metal surface is called work function  = hf . SI unit of work function is joule.
Energy of incident photon Work function Max K.E of electrons.