Question

How many electrons pass across a unit cross-sectional area of a conductor when a current of 0.5 mA flows in the conductor for 4 s?

Question 7Select one:

1.25
×
10
15


1.25
×
10
16


1.25
×
10
18


1.25
×
10
12

Answer 1

To find how many electrons pass across a unit cross-sectional area of a conductor when a current of 0.5 mA flows for 4 seconds, we can use the following formula:

\[
Q = I \times t
\]

Where:
- \( Q \) is the charge in coulombs,
- \( I \) is the current in amperes (A),
- \( t \) is the time in seconds (s).

1. Convert the current from milliamperes (mA) to amperes (A):
\[
I = 0.5 \, \text{mA} = 0.5 \times 10^{-3} \, \text{A} = 5 \times 10^{-4} \, \text{A}
\]

2. Calculate the total charge (\( Q \)) that flows in 4 seconds:
\[
Q = I \times t = 5 \times 10^{-4} \, \text{A} \times 4 \, \text{s} = 2 \times 10^{-3} \, \text{C}
\]

3. To find the number of electrons, we use the charge of an electron, which is approximately \( e = 1.6 \times 10^{-19} \, \text{C} \).

4. The number of electrons (\( n \)) can be calculated using the formula:
\[
n = \frac{Q}{e}
\]
\[
n = \frac{2 \times 10^{-3} \, \text{C}}{1.6 \times 10^{-19} \, \text{C/electron}} \approx 1.25 \times 10^{16} \, \text{electrons}
\]

So, the correct answer is:
\[
1.25 \times 10^{16}
\]

Thus, the answer is **1.25 × 10^16**.