Question

A cathode ray tube is used to study the behavior of electrons. As the emitted electrons impact on the fluorescent screen of the tube, they make the surface glow. These individual impacts can be used to count the number of electrons leaving the electron gun of the cathode ray tube each second. A group of students studying the electron emission has compiled a table show below.

time (min)	total number of electron impacts (x 1,000,000)
1	.212
2	.529
3	.711
4	1.12
5	1.70
6	1.91
7	2.09
8	2.51
9	2.71
10	3.10
11	3.21
12	3.71
13	3.79
14	4.20
15	4.67

Based on the data collected, what is the approximate magnitude and direction of the conventional current inside of the cathode ray tube?

• A. The current is approximately ${3.0910}^{5}Amperes$ toward the fluorescent screen of the tube.
• B. The current is approximately ${3.0910}^{5}Amperes$ away from the fluorescent screen of the tube.
• C. The current is approximately ${4.9610}^{14}Amperes$ toward the fluorescent screen of the tube.
• D. The current is approximately ${4.9610}^{14}Amperes$ away from the fluorescent screen of the tube.
• E. The current is approximately $8.27\times {10}^{-16}Amperes$ away from the fluorescent screen of the tube.

Answer 1

The correct option is E The current is approximately $8.27\times {10}^{-16}Amperes$ away from the fluorescent screen of the tube.

From recorded data we have , total number of electron impacts in 15 minutes or 900s ,

$=4.67\times {10}^6$ ,

total charge in the tube in 900s ,

by $q=ne=4.67\times {10}^6\times 1.6\times {10}^{-19}C$ ,

therefore current in tube will be ,

$I=q/t=4.67\times {10}^6\times 1.6\times {10}^{-19}/900=8.27\times {10}^{-16}A$ ,

as the directional current is taken opposite to the flow of electrons therefore current will be away from the fluorescent screen of the tube .