Question Detail

PHY 102 Test Compilation PHY 102 20 Objective Question
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Question

The weight of a charge-bearing oil droplet (carrying a charge of 10e) in an electric field in Millikan's apparatus is 2x10-14 N. If the droplet is located midway between plates 10 cm apart, determine the electric field strength needed to keep the droplet suspended.
Options
A 1.25 x 104 V/m
Correct Answer
B 2 x 104 V/m
C 2 x 10-14 V/m
D 1.25 x 105 V/m
Correct Answer

Option A is the correct answer.

Detailed Explanation

For the droplet to be suspended, the upward electric force balances its weight: qE = W, so E = W/q. Charge q = 10e = 10 x 1.6x10-19 = 1.6x10-18 C. E = W/q = (2x10-14)/(1.6x10-18) = 1.25x104 V/m. (The 10 cm plate separation is extra information not needed to find E here - it would be used to find the voltage V = E x d if asked.)

Hint

For the droplet to be suspended, the upward electric force balances its weight: qE = W, so E = W/q.

Question Info

Course: PHY 102
Topic: Test Compilation PHY 102 20
Type: Objective
Difficulty: Not specified
Question 1272 of 1819
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