Electric Fields and Potential Unit Test

Physics 12 Name: ______Version 1

Part A: Multiple Choice (2 marks each)

(1) What are the units of electric field strength?

a. N/C b. V/m c. both a. and b. d. neither a. nor b.

(2) What is the magnitude and direction of the electric field at point P?

4 4 a. 2.4 x 10 N/C left b. 2.4 x 10 N/C right 4 4 b. 3.0 x 10 N/C left d. 3.0 x 10 N/C right

5 (3) The electric field 20 mm from an unknown charge has a magnitude of 1.0 x 10 N/C. The magnitude of the electric field 10 mm from the charge is:

5 5 a. 4.0 x 10 N/C b. 2.0 x 10 N/C 4 4 c. 5.0 x 10 N/C d. 2.5 x 10 N/C

6 (4) A proton is accelerated from rest through a 1.0 x 10 volt potential difference. What speed does the proton attain?

4 7 a. 1.4 x 10 m/s b. 1.4 x 10 m/s 7 14 c. 1.9 x 10 m/s d. 1.9 x 10 m/s

(5) An electron accelerated in a vacuum through a potential difference of 'V' acquires a speed of 'v'. What speed does it acquire if the potential difference is '4V'?

a. 16 v b. 4 v c. 2 v d. v 2 (6) The potential difference between two parallel conducting plates is 8.7 x 10 V and –5 their separation is 0.400 cm. Find the work necessary to move 3.2 x 10 C of positive charge from the negative to the positive plate.

a. 0.0278 J b. 0.0295 J c. 6.95 J d. 2.78 J

-17 (7) A proton with kinetic energy of 2.1 x 10 J is moving into a region of charged parallel plates. The proton will be stopped momentarily in what region?

a. Region K b. Region L c. Region M d. Region N

(8) An electron moves from the negative plate to the positive plate in the situation shown below. It moves ______of the electric field and experiences a ______in potential energy.

a with the direction ; gain b. with the direction ; loss c. against the direction ; gain d. against the direction ; loss

Part B: Written Questions

(1) The nucleus of a helium atom contains 2 protons. An electron orbits the nucleus at a point 4.0 nm away. What is the magnitude and direction of the electric field at the location of the electron? (3 marks)

6 (2) An electron moving at 7.5 x 10 m/s enters an electric field between parallel plates by passing through a small hole in one of the plates as shown.

a) What is the impact speed on the second plate? Ignore friction. (4 marks)

b) If the plates are moved closer together, and the electron is released through again, will its impact speed be the same, greater, or less? ______(1 mark)

c) Explain using principles of Physics (2 marks). (3) A small 0.0021 kg plastic ball is suspended by a string in a uniform electric field as shown. Calculate the charge on the ball (4 marks)

(4) A helium nucleus having twice the charge and four times the mass of a proton is traveling with a high velocity when it enters a set of charged plates as shown.

What is the magnitude and direction of the acceleration of the nucleus? (4 marks)

6 BONUS: The plates are 1.0 m long and the nucleus enters at 1.5 x 10 m/s. What is the deflection of the helium nucleus just before it exits the plates? (1 mark)