# ICSE Worksheet for chapter-19 Thermionic Emission and Radioactivity class 10

#### Worksheet For class 10

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## Summary

1. Thermionic emission of hot cathode ray tube - Introduction; principle; deflection of charged particles by electric fields and florescence produced by electrons
2. Radioactivity and changes in the nucleus - Introduction; nucleus and its corresponding properties ; radioactivity as spontaneous disintegration α β γ ; harmful effects and safety precautions for radiations

### Section 1 - Objective

Q1. The minimum amount of energy required to emit electrons from a metal surface is called the:

1. Ionization energy
2. Dissociation energy
3. Cohesive energy
4. Work function

Q2. The work function of tungsten coated with barium oxide is nearly:

1. 5eV
2. 10eV
3. 1eV
4. 0.01eV

Q3. The electron emitter must have:

1. Low work function and low melting point
2. High work function and high melting point
3. High work function and low melting point
4. Low work function and high melting point

Q4. A TV tube requires an accelerating voltage of the order:

1. 150 volt
2. 1000 volt
3. 20 kV
4. 500 kV

Q5. Electrons was discovered by:

1. Neil Bohr
2. J.J. Thomson
3. R.A. Millikan
4. Rutherford

Q6. The charge on an atom is:

1. Positive
2. Negative
3. Neutral
4. None of these

Q7. Isotone of an element has –

1. Same number of electrons
2. Same number of protons
3. Same number of neutrons
4. Same number of neutrons and protons

Q8. An isotones of 32Ge76 is

1. 32 Ge77
2. 33Ge77
3. 36Ge77
4. 34Ge77

Q9. The triad of nuclei that is isotonic is:

1. 146C, 157N , 179F
2. 126C, 147N ,199F
3. 146C, 147N, 179F
4. 146C, 147N, 199F

Q10. An example of nuclear fusion reaction is:

1. 23390Th + 10n → 23490Th
2. 2713Al + 42He → 3015P + 10n
3. 32He + 32He → 42He + 211H
4. 23992U → 23993Np + 0-1e

Q11. Which particle is used to bombard 13Al28 to give 15P31 and a neutron?

1. α-particle
2. Deuteron
3. Proton
4. Neutron

Q12. Gamma rays are:

1. High energy electrons
2. Low energy electrons
3. High energy electromagnetic waves
4. High energy positrons

Q13. Which of the following radiation is least penetrating?

1. α-particles
2. β- particles
3. X-rays

Q14. Which of the following radiation suffers maximum deflection in a magnetic field ?

1. α-particles
2. β-particles
3. X-rays

### Section 2 - Subjective

Q1. Define the term work function of a metal

Q2. State any three properties of α ,β and γ rays.

Q3. What do you mean by thermionic emission? State its two properties

Q4. XRnY 86Po218 + alpha- particles. Find X And Y.

Q5. In the labelled diagram answer the following

• What is represented by symbols A, B, C, D and E?
• States the purpose of A,’B,C and D.

Q6. Give one use of radio – isotopes. What is meant by backgroung radiations?

Q7. Name a common device where a hot cathode ray tube is used.

• State the two properties which a substance should posses when used as thermionic emitter.

### Solutions: to worksheet-19 Topic-Thermionic Emission and Radioactivity

 1. D 2. C 3. D 4. C 5. B 6. C 7. C 8. B 9. A 10. C 11. A 12. C 13. A 14. B

#### Subjective Problems

4. X=88, Y = 222

5. (i) A – Indirectly heated cathode

B – Electron beam

C – Anode

D – Plates to apply electric field

E – Filament

(ii) Purpose:

A – indirectly heated cathode emits electrons by passing current in the filament.

B – waves on screen

C – anode imparts a large velocity to the electron beam passing through its hole.

D – electric field is produced by applying between the plates