dual nature of radiation and matter

Define field emission

By applying very strong electric field to a metal electrons can be pulled out of the metal as in a spark plug

Define photoelectric emission

When light of suitable frequency illuminates a metal surface ,electrons are emitted from the metal surface

The photo generated electrons are called photoelectrons

Who discovered the phenomenon of photo electric Emission

Heinrich Hertz

What did hertz observers on his investigation on the production of electromagnetic waves by mean of a spark discharge

He discovered the high voltage sparks by the means of a detector loop were enhanced when the emitter plate was illuminated by a uv light from an arc lamp

Define threshold frequency

When the frequency of incident light was smaller than a minimum value no electrons were emmited this minimum value is called threshold frequency

What does threshold frequency depend upon

It depends upon nature of material of the emitter plate

How can we change the frequency and intensity?

Light of different frequencies can be used by putting appropriate coloured filter or coloured glass path of the lights falling on the image. The intensity of light is varied by changing the distance of light source from the emitter

Why is collector a maintain positive potential with respect to the emitter C?

It is so that the electrons emitted from the ammeter C gets attracted towards collector A

Effect of intensity of light on photo current

It is found that photocurrent increases linearly with intensity of incident light

The number of photoelectrons emitted per second is directly proportional to the intensity of incident radiation

What is saturation current

The maximum value of photoelectric current is called saturation current

What happens to photoelectric current when a negative potentially supplied on plate A?

When Polarity reversed, the electrons are repelled and only sufficiently energetic electrons are able to reach collector A the photo current is found to decrease rapidly until it drops zero at a certain sharp. Please define a critical value of negative potential on plate.

Define stopping potential

The minimum negative potential at which the photocurrent stops or becomes zero is defined as cut-off or stopping potential

What does the maximum kinetic energy of Photoelectrons depend upon?

It depends on the light source and the amateur plate material, but is independent of intensity of incident radiation

What do we understand from the graph of variation of stopping potential with frequency of incident radiation for a Photos sensitive material?

1. The stopping potential Various linearly with frequency of incident radiation

2. There is a certain minimum cut-off frequency for which stopping potential is zero

What is an alternative name for minimum cut-off frequency?

Threshold frequency

Which photos sensitive material is more sensitive to light than zinc and copper

Selenium

Laws of photoelectric emission

• For a given photo, sensitive material and a frequency in incidentradiation greater than threshold of frequency, the photoelectric current is directly proportional to the Intensity of incident radiation

• For a given photo, sensitive material and frequency of incident radiation, the saturation current is want to be proportional to the intensity stopping independent of intensity of incident radiation

• For a given photo sensitive material, the system minimum cut-off frequency of incident radiation called Threshold frequency below which no mission a photocurrent takes place. No matter how intends the light is above, the threshold frequency, the stopping potential or equivalent Entally, maximum kinetic energy of the emitted photoelectrons increases linearly with the frequency of incident. Radiation is independent of intensity.

• The photoelectric emission is a mysterious process without any apparent time, lack, even when the Incident radiationis made exceeding