1.Define stopping potential?

Stopping potential is that value of the negative (retarding) potential given to the collecting electrode A which is just sufficient to stop the most energetic photoelectrons emitted and make the photocurrent zero

2.What is photo electric effect?

The ejection of electrons from a metal plate when illuminated by light or any other electromagnetic radiation

3.What is Bremsstrahlung?

When a fast moving electron penetrates and approaches a target nucleus, the interaction between the electron and the nucleus either accelerates or decelerates it which results in a change of path of the electron. The radiation produced from such decelerating electron is called Bremsstrahlung or braking radiation

4.How do we obtain characteristic x- ray spectra?

X-rays are produced when fast moving electrons strike the metal target. The intensity of the x-rays when plotted against its wavelength gives a curve called x-ray spectrum .

X-ray spectra consist of two parts: a continuous spectrum and a series of peaks superimposed on it.

The peaks are characteristics of the material of the target and hence it is called characteristic spectrum.

5.Define work function of a metal?Give its unit?

The minimum energy needed for an electron to escape from the metal surface is called work function of that metal. The work function of the metal is denoted by φ0 and is measured in electron volt (eV).

6.Uses/application of x-ray?(Any two points for two mark)

1) Medical diagnosis :  X-rays can pass through flesh more easily than through bones. Thus an x-ray radiograph containing a deep shadow of the bones and a light shadow of the flesh may be obtained. X-ray radiographs are used to detect fractures, foreign bodies, diseased organs etc.

2) Medical therapy : Since x-rays can kill diseased tissues, they are employed to cure skin diseases, malignant tumours etc.

3) Industry : X-rays are used to check for flaws in welded joints, motor tyres, tennis balls and wood. At the custom post, they are used for detection of contraband goods.

4) Scientific research : X-ray diffraction is important tool to study the structure of the crystalline materials – that is, the arrangement of atoms and molecules in crystals.

7.Define threshold frequency?

For a given surface, the emission of photoelectrons takes place only if the frequency of incident light is greater than a certain minimum frequency called the threshold frequency