Physics 12 - Quiz 3
1. A sphere of mass 2.5 ´10-10 kg, with a charge of 6.0 ´ 10-9 C, hangs from a thread as shown below. An external electric field of magnitude 2.0 ´10-1 N/C is directed upward.. Find the tension in the thread. (3 marks)
2. A - 2.3 ´10-6 C charge exerts a repulsive force of magnitude 0.35 N on an unknown charge 0.20 m away. What are the magnitude and polarity of the unknown charge? (2 marks)
3. A 4.0 ´ 10-9 C charge of mass 2.4 ´ 10-21 kg, is initially located at point A, 3.0 m from a stationary 6.0 ´10-8 C charge.
a) How much work is required, by an external agent, to move the 4.0 ´10-9 C charge to a point B, 0.50 m from the stationary charge? (3 marks)
b) If the 4.0 ´10-9 C charge is now released from point B, what will be its velocity when it passes back through point A? (2 marks)
4. Two point charges Q1 and Q2 are arranged as shown in the diagram below.
a) The electric potential at point P due to these charges is found to be 1.9´105 V. What are the magnitude and sign of charge Q1? (2 marks)
b) What is the potential difference between point P and point R, which is half way between point P and Q1? (3 marks)
5. Three charges are fixed as shown in the diagram below.
a) Calculate the net electric force, magnitude and direction, on Q2 due to Q1 and Q3. (3 marks)
b) Calculate the electric field strength, magnitude and direction, at the position of Q2. (2 marks)
6. A proton is accelerated from rest between parallel plates with a potential difference of 3.0 ´104 V.
a) What is the magnitude and direction of the electric field between the two plates? (2 marks)
b) What is the acceleration of the proton? (2 marks)
c) What is the proton's velocity upon reaching the negative plate? (1 mark)
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