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Mag Review

Mag Review. Question 1. Which pole of a compass needle points to a south pole of a magnet?. Answer. The North pole of a compass needle points to the South Pole because north is attracted to the south. Question 2. Outside a magnet the magnetic field lines are drawn from________ to _________.

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Mag Review

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  1. Mag Review

  2. Question 1 Which pole of a compass needle points to a south pole of a magnet?

  3. Answer • The North pole of a compass needle points to the South Pole because north is attracted to the south.

  4. Question 2 • Outside a magnet the magnetic field lines are drawn from________ to _________.

  5. Answer • From North to South

  6. Question 3 • Draw the magnetic field of the following magnet. • Is the field greater at point A or point B? A N S B

  7. Answer • The Magnetic Field is stronger at B because there is a greater concentration of magnetic field lines at point B N S

  8. Question 4 • When there is a change in the magnetic field in a closed loop of wire • A voltage is induced in the loop of wire. • Current is made to flow in the loop of wire • Electromagnetic induction occurs • All of these • None of these

  9. Answer • D • And a magnetic field is induced for the wire. According to Lenz’s Law that induced magnetic field will oppose the direction of the magnetic field that created the current

  10. Question 5 • When there is a change in the magnetic field in an open loop of wire • A voltage is induced in the loop of wire. • Current is made to flow in the loop of wire • Electromagnetic induction occurs • All of these • None of these

  11. Answer • E • Open circuit so no current will flow

  12. Question 6 • When a magnet is thrust into a coil of wire, the coil tends to • Attract the magnet as it enters • Repel the magnet as it enters • Both of these • Neither of these • Whose law is this?

  13. Answer • B because of Lenz’s Law

  14. Question 7 • Two electrons are in a region of space with no magnetic field. Electron A is at rest. Electron B is moving to the right at a constant velocity. A magnetic field directed into the page is then applied to the electrons. In which direction are each of the electrons moving after the field is applied?

  15. Answer • Charge A feels no affect because it is not moving at all so the v = 0 • Charge B will feel a force initially pushing it downward. From there it will start to spiral in a clockwise direction. Make sure you use your left hand for the eLEFTron.

  16. Question 8 • Two electrons are in a region of space with no magnetic field. Electron A is at rest. Electron B is moving to the right at a constant velocity. A magnetic field directed to the left is then applied to the electrons. In which direction are each of the electrons moving after the field is applied?

  17. Answer • Charge A feels no affect because it is not moving at all so the v = 0 • Charge B will feel no affect because the magnetic field is not perpendicular to the motion of the charge. You would have to break your hand to make the RHR work! RHR = Physics speak for Right hand rule!

  18. Question 9 • A proton is moving south as it enters a region that contains a magnetic field. It is deflected downward towards the earth. What is the direction of the magnetic field?

  19. Answer • From East to West • Red shows the direction of motion. • The charge is going into the page cause it is getting closer to the earth’s surface. • So the Magnetic Field is going in the direction shown in Orange

  20. Question 10 • Describe the path that a charged particle takes when it enters a magnetic field.

  21. Answer • It spirals!

  22. Question 11 • If a wire is carrying a current upward in a magnetic field pointing to the right, will it feel a force? If it does which direction will it get pushed?

  23. Answer • Out of the Page

  24. Question 12 • From the last question… • If the current is 10 A and the magnetic field 25 T, how long would the wire have to be to feel a force of 50 N?

  25. Answer • F=BiL • 50 N = (25 T) (10 A) L • L= .2 m

  26. Question 13 • If a charged particle is moving upward in a magnetic field that points inward and feels a force to the right is the particle positively or negatively charged?

  27. Answer • Negative • Check to see which hand can create this combination. Right means it is Positive. Left means it is negative

  28. Question 14 • What would be the radius of curvature for an electron that is moving at 3.45 x 10^6 m/s in a magnetic field of 60 T? • Remember that the charge of an electron is 1.6x10^-19C and the mass is 9.11x10^-31kg and yes, these numbers will be given on the test.

  29. Answer F= mv^2/r F=qvB mv^2/r=qvB (9.11x10^-31kg)(3.45 x 10^6 m/s)^2/r=(1.6x10^-19C)(3.45 x 10^6 m/s)(60T) r = 3.27 x 10^-7 m

  30. Question 15 • What would be the induced current in wire that is 10 m long if the magnetic field inducing it is 14 T and is moving at a speed of 12 m/s. The resistance in the wire is 6 ohms. Yes you do need that piece of information.

  31. Answer • Emf=Blv • Emf=(14T)(10m)(12m/s) • emf=1680 V • V=iR • 1680 V = i (6 ohms) • i=280 A

  32. Question 16 A transformer is plugged into an outlet with 100 turns on the primary and 10 turns on the secondary. What the current through a 10 ohm resistor connected to the secondary coil?

  33. Answer • Vp/Vs=Coils/Coils • 120V/Vs=100/10 • Vs=12V • V=IR • 12V=I (10 ohms) • 1.2 Amps

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