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Saturday, December 10, 2016

The diagram shows an oil droplet that has become charged by gaining five electrons.





Question 1
The diagram shows an oil droplet that has become charged by gaining five electrons. The droplet remains stationary between charged plates.



What is the magnitude and direction of the electrostatic force on the oil droplet?
A 5.0 × 10–15 N upwards
B 5.0 × 10–15 N downwards
C 5.0 × 10–13 N upwards
D 5.0 × 10–13 N downwards





Reference: Past Exam Paper – June 2008 Paper 1 Q31





Solution 1:
Answer: C.

Consider the forces acting on the charged oil droplet.

The weight of the oil droplets causes a downward force.
Being negatively charged (due to the electrons), the oil droplet is under an upward electrostatic force attracting it to the positive plate.


Electrostatic force = EQ        
where E is the electric field strength and Q is the total charge of the droplet


Electric field strength = V / d = 5000 / (0.8×10-2)
Total charge = 5 × charge of an electron = 5 × (1.6×10-19)


Electrostatic force = EQ = (V/d) × Q = 5.0 × 10-13 N

3 comments:

  1. What does "charge of an electric" mean here?
    where you multiplied 5*charge of an electric field

    ReplyDelete
    Replies
    1. it should be 'charge of an electron' instead of electric because it has gained 5 electrons

      thanks. it has been corrected above

      Delete
    2. Ahh, got it, many thanks

      Delete

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