Unit 3: Gravitational, Electric and Magnetic Fields Unit Test Name: Knowledge & Understanding Application Thinking & Inquiry Communication Total 15 18 5 6 44 Part 1: Multiple Choice 1. Two charged spheres are 5.00 cm apart. One sphere has a charge of 2.50 x 10-4 C and the other sphere has a charge of 3.20 x 10-5 C. The electric force between the two spheres is a. 1.44 x 10 1 N d. 2.88 x 10-4 N b. 4.44 x 10-20 N e. 4.44 x 10-18 N c. 2.25 x 10 19 N 2. Magnetic field strength is measured in a. N b. N C c. kg/c s d. kg m 2 /s 2 e. kg m/s 2 3. Which of the following diagrams represents the field of force around a negative point charge? a. d. b. e. c.
4. The value of g on Saturn is 10.9 N/kg. The weight of a 2.5 kg mass on Saturn is a. 2.5 kg d. 4.4 kg b. 4.4 N e. 27 N c. 11 N 5. A positively charged rod is brought close to a neutral pith ball hanging by a thread. The pith ball a. Becomes negatively charged d. Is attracted to the rod and then b. Is repelled by the rod and then repelled by the rod attracted to the rod e. Remains hanging by a thread c. Becomes positively charged motionless and unaffected by the rod. 6. In the diagram below, a permanent magnet is pulled upward through a horizontal loop of wire. Which of the following describes the induced current as viewed from above? a. Clockwise then counterclockwise d. Counter clockwise b. Clockwise e. No current is induced c. Counterclockwise then clockwise 7. A conductor is located between the poles of a horseshoe magnet. Current flows in the direction indicated by the arrow on the diagram. In which direction will the conductor move? a. Upward b. Downward c. Into the page d. Left e. Right
8. A proton of charge 1.6 x 10-19 C is moving east with a speed of 8.2 x 10 7 m/s, as it enters a magnetic field of 2.5 T downward. The magnitude and direction of the magnetic force acting on the proton is a. 3.3 x 10-11 N [N] b. 1.9 x 10 11 N [S] c. 5.3 x 10-12 N [S] d. 3.3 x 10-11 N [S] e. 1.9 x 10 11 N [N] 9. Which of the following statements about the loop shown below is false? (the loop is horizontally oriented). a. The north pole of the loop is at the bottom of the loop labelled Z. b. The direction of the magnetic field cannot be determined c. The magnetic field goes up through the loop d. The magnetic field is strongest in the inside of the loop e. The south pole of the loop is labelled X 10. Which of the following is NOT a similarity or difference between Coulomb s Law and Newton s Law of Universal Gravitation? a. The forces act along the line joining the centres of the masses or charges. b. The electric force can attract or repel, depending on the charges involved, whereas the gravitational force can only attract. c. The universal constant G is very small and in many cases the gravitational force can be ignored. Coulomb s constant k is very large, so that even small charges can result in noticeable forces. d. Coulomb s law is the product of two masses, whereas Newton s law of universal gravitation is the product of two charges e. The size of the force is the same as the force that would be measured if all the mass or charge was concentrated at a point at the centre of the sphere.
11. Which of the following diagrams most accurately depicts to field between two oppositely charged plates? a. d. b. e. c. 12. An object with a charge +q experiences an electric force FE when put in a particular location in the electric field ξ. The positive charge +q is removed and an object with charge -4q is placed in the same location in the electric field. This charge would feel an electric force of a. -2FE b. F E 2 c. 2F E q d. F E 4 e. -4FE 13. Given that in the diagram below, B is the magnetic field and v is the speed of the positive particle, what is the direction of the magnetic force? a. Right b. Out of the page c. Left d. Into the page e. Downward
14. If the point charge q in the diagram below was absent, the electric field at point B would be E. What is the electric field between the two point charges, -q and q, at point B which lies at the midpoint between the two charges? a. 2E [right] b. 0 c. 2E [left] d. ½ E [left] e. ½ E [right] 15. A sphere of charge +q is in a fixed position. A smaller sphere +q is placed near the larger sphere and released from rest. Which one of the following best describes its motion? a. Decreasing velocity and increasing acceleration b. Decreasing velocity and constant acceleration c. Increasing velocity and decreasing acceleration d. Increasing velocity and increasing acceleration e. Decreasing velocity and decreasing acceleration
Short Answer 16. Explain the process of charging by induction using a positive rod, an electroscope, and a wire. Be sure to mention the movement of charges and the final charge on the electroscope. 17. A charged particle moving along the + y-axis passes through a uniform magnetic field oriented in the =z direction. A magnetic force acts on the particle in the x direction. Does the particle have positive charge or negative charge? How would the force change if the charge of the particle were to triple? Explain.
Problems 16. The International Space Station (ISS) orbits the Earth at an altitude of about 350 km above Earth s surface. a. Determine the speed needed by the ISS to maintain its orbit. b. Determine the orbital period of the ISS in minutes.
17. A ping-pong ball of mass 3.0 x10-4 kg is hanging from a light thread 1.0 m long, between two vertical parallel plates 10 cm apart, as shown. When the potential difference across the plate is 420 V, the ball comes to equilibrium 1.0cm to one side of its original position. a. What is the electric field intensity between the plates? b. What is the tension in the thread? c. What is the magnitude of the electric force deflecting the ball? d. What is the charge on the ball?
18. An electron starts from rest. A horizontally directed electric field accelerates the electron through a potential difference of 37 V. The electron then leaves the electric field and moves into a magnetic field. The magnetic field strength is 0.26 T, directed into the page, as shown below, and the mass of the electron is 9.11 x 10-31 kg. a. Determine the speed of the electron at the moment it enters the magnetic field. b. Determine the magnitude and direction of the magnetic force on the electron. c. Determine the radius of the electron s circular path.