Question
Why are materials of low work function preferred as thermionic cathode materials?
✓
Answer
By using materials of low work functions, the emission of electrons from such a surface takes place at relatively low temperature (at 1700°C in instead of 2500°C approximately).
Need a full question paper?
Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.
Explore more
Similar questions
(a) State the SI unit of specific resistance.
(b) Four resistance A, B, C and D of resistance $3 \Omega$ each are joined to form a square. Calculate the equivalent resistance between the opposite ends of the square
→(b) Four resistance A, B, C and D of resistance $3 \Omega$ each are joined to form a square. Calculate the equivalent resistance between the opposite ends of the square
What is a single movable pulley? What is its mechanical advantage in the ideal case?
(a) What do you understand by the term electric work?
(b) (i) Which part of an electrical appliance is earthed?
(ii) State a relation between electrical power, resistance and potential difference in an electrical circuit.
(b) (i) Which part of an electrical appliance is earthed?
(ii) State a relation between electrical power, resistance and potential difference in an electrical circuit.
A 200 v electric transfer draws an electric current of 11 A. What is its electrical resistance?
Two musical notes of the same pitch and same loudness are played on two different instruments. Their wave patterns are as shown in following Figure.
Explain why the wave patterns are different.
Explain why the wave patterns are different.
What is meant by a torque?
State the S.I. units of electrical power and electrical energy.
(i) Define the household unit of electricity.
(ii) What is the voltage of the electricity that is generally supplied to a house?
(i) Define the household unit of electricity.
(ii) What is the voltage of the electricity that is generally supplied to a house?
(a) Why is the base of a cooking pan generally made thick?
(b) Why does stone lying in the sum get heated up much more than water lying for the same duration of time?
(b) Why does stone lying in the sum get heated up much more than water lying for the same duration of time?
Which type of lever has a mechanical advantage always more than one? Give one example. What change can be made in this lever to increase its mechanical advantage?
\text { Fig } 3.16 \text { below shows a lever in use. }
(a) To which class of lever does it belong?
(b) If $A B=1 m , A F=0.4 m$, find its mechanical advantage,
(c) calculate the value of $E$.
→(a) To which class of lever does it belong?
(b) If $A B=1 m , A F=0.4 m$, find its mechanical advantage,
(c) calculate the value of $E$.