Home > Chemistry MCQ: Questions and Answers for Competitive Exams > In which direction do positive rays travel in a discharge tube with a perforated cathode?
In which direction do positive rays travel in a discharge tube with a perforated cathode?
A
Parallel to the anode
B
Parallel to the cathode
C
From cathode to anode
D
From anode to cathode
Correct Answer:
D
From anode to cathode
When a discharge tube is filled with a gas at low pressure and a high voltage is applied, the gas gets ionised. Electrons released from the cathode move toward the anode, colliding with neutral gas atoms along the way. These collisions knock off more electrons and leave behind positively charged ions, which naturally get pulled toward the negatively charged cathode since opposite charges attract each other.
- Since the cathode has small holes or perforations, most positive ions coming from the anode side pass right through it and continue moving in a straight line behind the cathode
- This is why they're called "positive rays" or "canal rays" — canal referring to the holes they travel through
- Their direction of motion is always from the anode toward the cathode, exactly opposite to the direction electrons travel
- Goldstein's canal-ray experiment (1886) led to the discovery of positively charged particles and later contributed to the identification of the proton