How many of the following statement are true about the cathode rays?
(i) Path of travelling is straight from the cathode with a very high velocity as it produces shadow of an object placed in its path
(ii) Rays consist of material particle.
(iii) They deflect towards negative end of the electrode.
(iv) They produce yellow glow when the glass will beyond anode.
(v) Cathode rays penetrate through thin sheets of aluminium and metals.
(vi) They affect the photographic plates
(vii) The ratio of charge (e) to mass (m) i.e. charge//mass is same for all cathode rays irrespective of the gas used in the tube. `e//m=1.76xx10^(11) Ckg^(-1)`
(viii) Cathode rays are visible at low voltage.

Answer

To determine how many of the statements about cathode rays are true, we will evaluate each statement one by one.

### Step-by-Step Solution:

1. **Statement (i)**: "Path of travelling is straight from the cathode with a very high velocity as it produces shadow of an object placed in its path."
- **Evaluation**: True. Cathode rays, which are streams of electrons, travel in straight lines and can produce shadows when an object is placed in their path.

2. **Statement (ii)**: "Rays consist of material particle."
- **Evaluation**: True. Cathode rays are indeed composed of electrons, which are material particles.

3. **Statement (iii)**: "They deflect towards negative end of the electrode."
- **Evaluation**: False. Cathode rays consist of negatively charged electrons and will deflect towards the positive end of the electrode, not the negative end.

4. **Statement (iv)**: "They produce yellow glow when the glass will beyond anode."
- **Evaluation**: False. Cathode rays produce fluorescence when they strike a material, but they do not produce a glow when they are beyond the anode.

5. **Statement (v)**: "Cathode rays penetrate through thin sheets of aluminium and metals."
- **Evaluation**: True. Cathode rays can penetrate thin sheets of materials like aluminum, although they cannot penetrate thick materials.

6. **Statement (vi)**: "They affect the photographic plates."
- **Evaluation**: True. Cathode rays can expose photographic plates, indicating their effect on them.

7. **Statement (vii)**: "The ratio of charge (e) to mass (m) i.e. charge/mass is same for all cathode rays irrespective of the gas used in the tube. e/m = 1.76 x 10^11 C/kg."
- **Evaluation**: True. The charge-to-mass ratio for cathode rays (electrons) is constant regardless of the gas used in the tube.

8. **Statement (viii)**: "Cathode rays are visible at low voltage."
- **Evaluation**: False. Cathode rays are not visible to the naked eye and can only be detected through their effects, such as fluorescence or heating.

### Summary of True Statements:
- True Statements: (i), (ii), (v), (vi), (vii)
- False Statements: (iii), (iv), (viii)

### Conclusion:
Out of the eight statements, **five statements are true**.