MCAT Physics Question 64: Answer and Explanation
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Question: 64
4. If the electric field at a distance r away from charge Q is what is the ratio of the electric fields at r, 2r, and 3r?
- A. 9:03:01
- B. 36:09:04
- C. 36:18:09
- D. 36:18:12
Correct Answer: B
Explanation:
The first step in answering this question is to remember that the magnitude of the electric field is inversely proportional to the square of the distance:
Therefore, if the electric field at radius r, Er, is
then the electric field at radius 2r will be
Similarly, the electric field at radius 3r is equal to
Therefore, the ratio of Er:E2r:E3r is 36:9:4.