Let's solve
Question 4 and
Question 5 step by step.
---
✔ Question 4: Cathode Ray Tube (CRT)
####
(a) Label the diagram of the CRT
The diagram shows a cathode ray tube with one label already given:
Y-plates. We need to label the other five features.
Here’s what each part is:
1.
Leftmost component (coil-like structure):
→
Heater / Filament
*(This heats the cathode to emit electrons.)*
2.
Next to heater, inside the tube:
→
Cathode
*(Emits electrons when heated.)*
3.
After cathode, small metal cylinder:
→
Anode (or Accelerating Anode)
*(Accelerates the electrons toward the screen.)*
4.
Between anode and Y-plates:
→
X-plates
*(Used for horizontal deflection of electron beam.)*
5.
Far right end (screen):
→
Fluorescent screen
*(Where the electron beam hits and produces a visible spot.)*
So, labeling from left to right:
- Top-left box:
Heater
- Bottom-left box:
Cathode
- Middle-bottom box:
Anode
- Top-right box:
X-plates
- Bottom-right box:
Fluorescent screen
✔ Answer (a):
```
[Heater] [Y-plates] [X-plates]
[Cathode] [Anode] [Fluorescent screen]
```
---
####
(b) State what occupies the rest of the space inside the Cathode Ray Tube.
The inside of the CRT is evacuated to remove air molecules that could interfere with the electron beam.
✔ Answer (b):
Vacuum (or low pressure gas)
> This ensures electrons can travel freely without colliding with air particles.
---
####
(c) Briefly explain what causes the cathode to emit cathode rays.
The cathode emits electrons due to
thermionic emission — when the cathode is heated by the filament, electrons gain enough energy to escape from the metal surface.
✔ Answer (c):
When the cathode is heated, electrons are emitted from its surface due to thermionic emission.
---
####
(d) What are cathode rays?
Cathode rays are streams of high-speed
electrons emitted from the cathode.
✔ Answer (d):
Cathode rays are beams of fast-moving electrons.
---
####
(e) Name the process taking place at the cathode.
As explained above, it's
thermionic emission.
✔ Answer (e):
Thermionic emission
---
####
(f) Give an example of a use for a cathode ray tube.
Historically used in:
- Old television sets
- Oscilloscopes
- Computer monitors (older models)
✔ Answer (f):
Oscilloscope or
Old TV screen (any valid example)
---
✔ Total for Question 4: 10 marks
---
✔ Question 5: Radioactive Decay – Barium Isotope
> A radioactive isotope of barium has a half-life of
2 minutes.
> Initial activity =
200 disintegrations per minute
> Find the activity after
6 minutes.
---
#### Step-by-step:
Half-life (T½) = 2 minutes
Time elapsed = 6 minutes
Number of half-lives = 6 ÷ 2 =
3 half-lives
Each half-life reduces the activity by half.
Initial activity = 200 dpm
After 1st half-life: 200 ÷ 2 = 100
After 2nd half-life: 100 ÷ 2 = 50
After 3rd half-life: 50 ÷ 2 =
25
✔ Answer (5):
25 disintegrations per minute
---
✔ Final Answers Summary:
---
Question 4
(a) Labels:
- Top-left:
Heater
- Bottom-left:
Cathode
- Middle-bottom:
Anode
- Top-right:
X-plates
- Bottom-right:
Fluorescent screen
(b) Vacuum (or low-pressure environment)
(c) Heating the cathode causes thermionic emission, releasing electrons.
(d) Beams of fast-moving electrons.
(e) Thermionic emission
(f) Example: Oscilloscope or old TV screen
---
Question 5
(Activity after 6 minutes):
25 disintegrations per minute
---
✔ All questions solved!
Let me know if you'd like this formatted as a printable answer sheet.
Parent Tip: Review the logic above to help your child master the concept of radioactivity worksheet.
