CHAPTER 5 Test B Lsn 5-6 to 5-8 TEST REVIEW

Transcription

1 IB PHYSICS Name: Period: Date: DEVIL PHYSICS BADDEST CLASS ON CAMPUS CHAPTER 5 Test B Lsn 5-6 to 5-8 TEST REVIEW 1. This question is about electric circuits. (a) (b) Define (i) (ii) electromotive force (emf ) of a battery. electrical resistance of a conductor. A battery of emf ε and negligible internal resistance is connected in series to two resistors. The current in the circuit is I. (i) State an equation giving the total power delivered by the battery. (ii) The potential difference across resistor R 1 is V 1 and that across resistor R 2 is V 2. Using the law of the conservation of energy, deduce the equation below. ε = V 1 + V 2 Chap5 Test B Lsn 5-6 To 5-8 Test Review Page 1 of 10

2 (c) The graph shows the I-V characteristics of two conductors, X and Y. On the axes below, sketch graphs to show the variation with potential difference V of the resistance of conductor X (label this graph X) and conductor Y (label this graph Y). You do not need to put any numbers on the vertical axis. (d) The conductors in (c) are connected in series to a battery of emf ε and negligible internal resistance. (3) The power dissipated in each of the two resistors is the same. Chap5 Test B Lsn 5-6 To 5-8 Test Review Page 2 of 10

3 Using the graph given in (c), (i) (ii) determine the emf of the battery. calculate the total power dissipated in the circuit. 2. The graph shows the variation with time t of the magnetic flux φ through a coil that is rotating in a uniform magnetic field. The magnitude of the emf induced across the ends of the coil is maximum at time(s) A. t 1 and t 3. B. t 2 and t 4. C. t 3 only. D. t 4 only. 3. A sinusoidal ac power supply has rms voltage V and supplies rms current I. What is the maximum instantaneous power delivered? A. 2VI B. 2 VI C. VI D. VI 2 Chap5 Test B Lsn 5-6 To 5-8 Test Review Page 3 of 10

4 4. A copper sheet is suspended in a region of uniform magnetic field by an insulating wire connected to a horizontal support. The sheet is pulled to one side so that it is outside the region of the field, and then released. The uniform magnetic field is directed into the plane of the paper. Which of the following is true for both the direction of the induced current in the sheet and the change in amplitude of the oscillations of the sheet with time? Direction of induced current Change in amplitude A. stays the same no change B. changes decreases C. stays the same decreases D. changes no change 5. This question is about a generator. (a) (b) Define electromotive force The graph shows the variation with time of electromotive force (emf) for a generator. Chap5 Test B Lsn 5-6 To 5-8 Test Review Page 4 of 10

5 (i) (ii) (iii) Calculate the rms value of the emf of the generator. The speed of rotation of the generator is halved with no other changes being made. On the graph, sketch the variation of emf with time. Explain why the graph you drew in (ii) is different from the original graph. 6. A magnetic field of strength B links a coil. The direction of the field is normal to the plane of the coil. The graph shows how B varies with time t. Which of the following graphs shows how the induced emf ε in the coil varies with t? Chap5 Test B Lsn 5-6 To 5-8 Test Review Page 5 of 10

6 7. The graph shows the variation of the induced emf ε of a generator as a function of time. The frequency of rotation of the generator is halved. Which of the following graphs correctly shows the variation of the new induced emf ε as a function of time? Chap5 Test B Lsn 5-6 To 5-8 Test Review Page 6 of 10

7 8. This question is about induced emf and transformers. (a) (b) One of the coils of a particular transformer is connected in series with a switch and a battery. The coil has low resistance. On closing the switch it is observed that the current takes a certain amount of time to reach its final constant value. Explain this observation with reference to Faraday s law and Lenz s law In a particular power station the voltage generated is stepped up by a transformer. The root mean square voltage is increased by a factor of The output power of the transformer is transmitted to a town by cables. (i) (ii) Outline what is meant by the root mean square value of a time-varying voltage. State the best estimate for the factor by which the power loss in the cables is reduced as a result of stepping up the voltage. 9. A permanent bar magnet is moved towards a coil of conducting wire wrapped around a non-conducting cylinder. The ends of the coil, P and Q are joined by a straight piece of wire. (3) The induced current in the straight piece of wire is A. alternating. B. zero. C. from P to Q. D. from Q to P. Chap5 Test B Lsn 5-6 To 5-8 Test Review Page 7 of 10

8 10. Electromagnetic induction (a) (b) State Lenz s law A long solenoid is connected in series with a battery and a switch S. Several loops of wire are wrapped around the solenoid close to its midpoint as shown below. The ends of the wire are connected to a high resistance voltmeter V that has a centre zero scale (as shown in the inset diagram). The switch S is closed and it is observed that the needle on V moves to the right and then drops back to zero. Describe and explain, the deflection on the voltmeter when the switch S is re-opened. Description: Explanation: 11. Raoul suggests that power losses in a transformer may be reduced by the following. I. Constructing the core from a solid block of steel. II. III. Using large diameter wire in the coils. Using wire of low resistivity. Which of the above suggestions would reduce power loss? A. I only B. II only C. II and III only D. I, II and III (4) Chap5 Test B Lsn 5-6 To 5-8 Test Review Page 8 of 10

9 12. A rectangular loop of conducting wire rotates in a region of magnetic field. The graph shows the variation with time t of the induced emf in the loop during one cycle. The resistance of the coil is 5.0 Ω. Which of the following is the average power dissipated in the loop? A. 45 W 2 B. 45 W 2 C. 45 W D W 13. An AC generator produces a voltage of peak value V. The frequency of rotation of the coil of the generator is doubled. The rms value of the voltage produced is V A V B.. 2 C. V 2. D. 2V This question is about alternating current. (a) The graph shows the variation with time t of the output voltage V of an ac generator of negligible internal resistance. Chap5 Test B Lsn 5-6 To 5-8 Test Review Page 9 of 10

10 (b) A resistor of resistance 25 Ω is connected across the output of the generator. Calculate (i) (ii) (iii) the rms value of the current in the resistor. the average power dissipated in the resistor. the power dissipated in the resistor at 0.40 ms. The frequency of rotation of the generator coil is now doubled. Sketch, using the axes in (a), the variation with t of the new output voltage V. Chap5 Test B Lsn 5-6 To 5-8 Test Review Page 10 of 10