MHT-CET : Physics Entrance Exam

### MHT - CET : Physics - Thermionic Emission Know More

1.      The Constants of the Triode:

1.      Amplification Factor: It is the ratio of the change in plate voltage to the change in grid voltage for a constant plate current.

 m = dVp Ip = constant. The amplification factor m has no unit. dVg

2.

3.      Transconductance: It is the ratio of the change in plate current to the change in grid voltage for a constant plate voltage.

 gm = dIp Vp = constant. The unit of transconductance gm is mho or siemens. dVg

4.

5.      Plate Resistance: It is the ratio of change in plate voltage to the change in plate current when the grid voltage is kept constant.

 rp = dVp Vg = constant. dip

2.

3.      Relation between Triode Constants: m = rp × gm.

4.      The 'Child-Langmuir Law': In the space charge region of the vacuum diode characteristic, the relation between the plate current (Ip) and the plate potential (Vp) is given approximately by the 'Child-Langmuir Law' which is as follows:

Ip = KV
p3/2,

 where Ip = plate current K = constant Vp = plate potential

5.

 Vacuum diode characteristic

6.

 Career in India | Jobs in India