When the pressure of the gas in a discharge tube is gradually lowered. I. there is a violet glow in the tube II. the glow in the tube splits into bands which get further apart. III, the glow and the bands eventually disappear and there is a green fluorescence in the tube. IV. the tube breaks into pieces. Which of the following are correct?
I and II only
I and III only
I and IV only
I, II and III only
I, II III and IV
Explanation
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I presumed the answer is : D
Explanations
As the pressure of the gas in a discharge tube is gradually lowered, the behavior of the glow and the resulting phenomena depend on the state of the gas and the discharge conditions.
Let's analyze each statement:
1. There is a violet glow in the tube:
At high pressure, the discharge tube typically emits a violet glow due to the ionization of the gas and the transition of electrons between energy levels.
2. The glow in the tube splits into bands which get further apart:
As the pressure is lowered, the glow often becomes more diffuse and can split into spectral lines or bands due to the electron transitions in the excited atoms of the gas. These bands get farther apart as the pressure decreases because the excitation of atoms becomes more specific.
3. The glow and the bands eventually disappear and there is a green fluorescence in the tube:
At even lower pressures, the gas may reach a point where the discharge is no longer sustained, and a different type of emission (such as fluorescence) may appear. The green fluorescence could be from certain gases (like mercury or others) in the discharge tube.
4. The tube breaks into pieces:
If the pressure is extremely low, the conditions in the discharge tube might cause mechanical instability, but this typically occurs only under specific conditions, such as over-pressurization or incorrect handling, rather than just from a gradual decrease in pressure.
Conclusion:
The first three statements (I, II, and III) describe the expected behavior of the glow as pressure decreases. Statement IV is less likely to occur from just the lowering of pressure.
Answer: D. I, II, and III only
