AP Physics Electricity and Magnetism #5 Capacitors, Magnetic Force

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Georgia Strickland
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1 Name Period AP Physics Electricity and Magnetism #5 Capacitors, Magnetic Force Dr. Campbell 1. A 3.00 µf and 4.00 µf capacitor are connected in series, and this combination is connected in parallel with a 2.00 µf capacitor (see Fig 19-52, page 549). What is the net capacitance? What is the voltage on each capacitor? 3.71 µf, 26.0 V, 14.9 V, 11.1 V 2. (a) Six 4.7 µf capacitors are connected in parallel. What is the equivalent capacitance? (b) What is their equivalent capacitance in series? 28.2 µf, 0.78 µf 3. Alpha particles of charge q = +2e and mass m= 6.6 x kg are emitted from a radioactive source at a speed of 1.6 x 10 7 m/s. What magnetic field strength would be required to bend them into a circular path of radius r = 0.25 m? 1.3T 1

2 4. Find the direction of the force on a negative charge for each diagram shown in Fig 20-51, page 578, where V (green) is the velocity of the charge and B is the direction of the magnetic field. a. b. c. d. e. f. 5. Determine the direction of B for each case in Fig 20-52, page 578, where F represents the maximum magnetic force on a positively charged particle moving with velocity v. a. b. c. 6. An electron experiences the greatest force as it travels 2.9 x 10 6 m/s in a magnetic field when it is moving northward. The force is upward and of magnitude 7.2 x N. What are the magnitude and direction of the magnetic field? 1.6 T East 7. A doubly charged helium atom whose mass is 6.6 x kg is accelerated by a voltage of 2100 V. (a) What will be its radius of curvature if it moved in a plane perpendicular to a uniform T field? (b) What is its period of revolution? m, 3.8 x 10-7 s 2

3 8. A 3.40 g bullet moves with a speed of 160 m/s perpendicular to the Earth s magnetic field of 5.00 x 10-5 T. If the bullet possesses a net charge of 13.5 x10-9 C, by what distance will it be deflected from it path due to the Earth s magnetic field after it has traveled 1.00 km? 6.2 x 10-7 m 9. A proton of mass m p and charge e is in a box that contains an electric field E, and the box is located in Earth's magnetic field B. The proton moves with an initial velocity vertically upward from the surface of Earth. Assume gravity is negligible. (a) On the diagram above, indicate the direction of the electric field inside the box so that there is no change in the trajectory of the proton while it moves upward in the box. Explain your reasoning. (b) Determine the speed v of the proton while in the box if it continues to move vertically upward. Express your answer in terms of the fields and the given quantities. 3

4 The proton now exits the box through the opening at the top. (c) On the diagram above, sketch the path of the proton after it leaves the box. (d) Determine the magnitude of the acceleration a of the proton just after it leaves the box, in terms of the given quantities and fundamental constants. 10. A uniform magnetic field of magnitude B = 1.2 teslas is directed toward the bottom of the page in the -y direction, as shown above At time t = 0, a proton p in the field is moving in the plane of the page with a speed v 0 = 4 x 10 7 meters per second in a direction 30 above the +x axis. a. Calculate the magnetic force on the proton at t = 0. b. With reference to the coordinate system shown above on the right, state the direction of the force on the proton at t = 0. 4

5 c. How much work will the magnetic field do on the proton during the interval from t = 0 to t = 0.5 second? d. Describe (but do not calculate) the path of the proton in the field. 11. In region I shown above, there is a potential difference V between two large, parallel plates separated by a distance d. In region II, to the right of plate D, there is a uniform magnetic field B pointing perpendicularly out of the paper. An electron, charge -e and mass m, is released from rest at plate C as shown, and passes through a hole in plate D into region II. Neglect gravity. a. In terms of e, V, m, and d, determine the following. i. The speed v 0 of the electron as it emerges from the hole in plate D 5

6 ii. The acceleration of the electron in region I between the plates Dr. Campbell b. On the diagram below do the following. i. Draw and label an arrow to indicate the direction of the magnetic force on the electron as it enters the constant magnetic field. ii. Sketch the path that the electron follows in region II. c. In terms of e, B. V, and m, determine the magnitude of the acceleration of the electron in region II. 6

Physics 30 Worksheet #10 : Magnetism From Electricity

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