simple T/F questions. Please solve ALL of them, unless not worth it. Thanks in a

Question

simple T/F questions.

Please solve ALL of them, unless not worth it.

Thanks in advance.

Inductance

1.( ) Similar to that fact that mass means inertia, i. e. anything with mass tend to oppose velocity change, the self-inductance L means a coil’s tendency to oppose current change.

2. ( ) m a=F, the bigger the mass, the harder it is to get acceleration.

3. ( ) di/dt is like the acceleration for current. –L dI/dt =L , the larger the inductance L, the smaller the di/dt, (the harder it is to change the current in the coil) .

4. ( ) The inductance L is related to how fast an external magnetic field’s flux is changing.

5. ( ) The inductance L is not related to any external magnetic field. When a coil’s current changes, the B field created by itself changes, and the flux going through itself changes, hence an induced emf L=–L dI/dt occurs.

6. ( ) By definition of L, L= –L di/dt, also L= –N dB/dt. Hence, L=N(dB/dt)/ (dI/dt) =NB/I.

7.( ) L of a given coil changes at different current.

8.( ) L of a given coil is proportional to the number of coil and the ration between the flux due to the B field created by its own current and the current value. So L is determined by the area and shape of the coil, as well as the number of turns, and it is not affected by the current.

9.( ) When you double the current in a coil, the B field doubles; and the flux doubles. But the ration of B/I stay unchanged, so L is independent from the current. L is an intrinsic property of a given coil.

10.( ) L has unit H, Henry. 1H =1 Vs/A

11. ( ) L has unit H, Henry. 1H =1 VA/s

12.( ) current I is similar to velocity=dx/dt in mechanics.

13.( ) current I=dq/dt is similar to acceleration in mechanics.

14.( ) current’s change rate dI/dt is similar to acceleration in mechanics.

LC circuit

15. ( ) A coil is similar to a spring, and it stores electrical potential energy.

16.( ) A capacitor is similar to a spring, and it stores electrical potential energy. U=Q2 /2C, where Q is like x and 1/C is like the spring constant k.

17. ( ) A capacitor is similar to a spring, when voltage is applied, it store change Q=V/C, where Q is like the stretched distance for the spring, x; 1/x is like the spring constant k and the applied voltage is like the applied force. |x|=|F|/k

18. ( ) The amount of energy stored in a capacitor is stored in the E field, which is like a kinetic energy.

19. ( ) The amount of energy stored in a capacitor is stored in the E field, which is like a potential energy.

20. ( ) A coil is similar to a mass, and when it has current it has B field related energy (1/2 L I2 ), which is similar to the kinetic energy in mechanics.

21. ( ) The amount of energy associated with an inductor is in the B field, which is like a potential energy.

22. ( ) The amount of energy associated in an inductor is in the B field, which is like a kinetic energy, when charges stop moving and the current is zero, this energy becomes zero.

23. ( ) When an inductor (coil) is connected to a charged capacitor, it is like when a mass is connected to a stretched spring. The capacitor will start to discharge, and the current will increase gradually, converting electrical potential energy to magnetic energy in the inductor (1/2 L I2 ). Just like the spring will shrink toward its natural length, and the mass will speed up, converting potential energy (1/2 k x2 ) into kinetic energy (1/2 m v2 ).

24. ( ) When an inductor (coil) is connected to a charged capacitor, it is like when a mass is connected to a stretched spring. The capacitor will start to discharge, and the current will increase gradually, converting energy from the inductor to the capacitor. Just like the spring will shrink toward its natural length, and the mass will speed up, converting potential energy (1/2 k x2 ) into kinetic energy (1/2 m v2 ).

25. ( ) Once the spring shrinks to its natural length the potential energy and spring force becomes zero, but the mass now has the maximum speed and will not stop. It will compress the spring until all the kinetic energy is converted into potential energy stored in the spring. At that time the spring will be compressed by the same amount of the amplitude. Similarly, when the capacitor is 100% discharged, the current in the circuit reaches its maximum and will not stop right away, due to the inductor, hence charging the capacitor in the opposite way until all the 1/2 L I2 energy is converted in to the capacitor energy. At that time the capacitor has the same amount of the charge as the initial maximum charge, but the positive and negative plates flipped.

26. ( ) When an inductor (coil) is connected to a charged capacitor, it is like when a mass is connected to a stretched spring. The capacitor will start to discharge. When the capacitor is 100% discharged, the current in the circuit reaches its maximum and will not stop right away, due to the inductor, hence charging the capacitor in the opposite way until all the 1/2 L I2 energy is converted in to the capacitor energy. At that time the capacitor has the same amount of the charge as the initial maximum charge, and the positive and negative plates will be the same.

27. ( ) When an inductor (coil) is connected to a charged capacitor, it is like when a mass is connected to a stretched spring. The capacitor will start to discharge. When the capacitor is 100% discharged, the current in the circuit becomes zero.

28. ( )Once all energy is converted into electrical potential energy and the capacitor is fully changed again (reversely), the current will stop and the system will stay like that.

29. ( )Once all energy is converted into electrical potential energy and the capacitor is fully changed again (reversely), the current will flip direction to discharge the capacitor and keep repeating that to form periodic oscillations.

30. ( ) The maximum energy stored in the capacitor is ½ Q2 max/C=½ CVmax 2 is equal to the maximum energy associated with the current (B field ) in the inductor, ½ LImax 2 =½ CVmax 2 = ½ Q2 max/C

31. ( ) At any time the energy stored in the capacitor is ½ Q2 /C=½ CV 2 is equal to the energy associated with the current (B field ) in the inductor, ½ LI 2 =½ CV2 =½ Q2 /C.

32. ( ) At any time the energy stored in the capacitor is plus the energy associated with the current (B field ) in the inductor stays unchanged. ½ LI 2 + ½ CV2 = constant = ½ LImax 2 =½ CVmax 2 = ½ Q2 max/C

33. ( ) In the LC circuit, the current and capacitor voltage reaches the maximum at the same time.

34. ( ) In the LC circuit, when the current reaches the maximum, the capacitor has no charge and voltage.

35. ( ) In the LC circuit, when the capacitor charge and voltage reaches the maximum, the current is zero.

36. ( ) When an inductor (coil) is connected to a charged capacitor, it takes 1/2 period for the capacitor to fully discharge.

37. ( ) When an inductor (coil) is connected to a charged capacitor, it takes ¼ period for the capacitor to fully discharge.

38. ( ) When an inductor (coil) is connected to a charged capacitor, it takes 1/2 period for the current to reach the maximum.

39. ( ) When an inductor (coil) is connected to a charged capacitor, it takes ¼ period for the current to reach the maximum.

40. ( ) When an inductor (coil) is connected to a charged capacitor, it takes 1/2 period for the capacitor to be fully charged with opposite signs.

41. ( ) When an inductor (coil) is connected to a charged capacitor, it takes 1 period for the capacitor to be fully charged with opposite signs.

42. ( ) When an inductor (coil) is connected to a charged capacitor, it takes 1/2 period for the current to first become zero again.

43. ( ) When an inductor (coil) is connected to a charged capacitor, it takes 1 period for the current to FIRST become zero again.

44. ( ) Similar to T=2 sqrt(m/k), the period of the LC circuit is T=2 sqrt(L/C).

45. ( ) Similar to T=2 sqrt(m/k), the period of the LC circuit is T=2 sqrt(LC). Because C is similar to 1/k. The larger the values of inductance and/or the capacitance, the longer the LC oscillation period is.

46. ( ) Similar to = sqrt(k/m), the angular frequency of the LC circuit is = sqrt(C/L).

47. ( ) Similar to = sqrt(k/m), the angular frequency of the LC circuit is =1/sqrt(LC). Because C is similar to 1/k. The larger the values of inductance and/or the capacitance, the faster the LC oscillation frequency is.

48. ( ) The frequency and period of the LC circuit oscillation is related to the initial condition (initial amount of capacitor charges or current in the circuit).

49. ( ) The frequency and period of the LC circuit oscillation is independent to any initial condition (initial amount of capacitor charges or current in the circuit), and only determined by the values of L and C.

50. ( ) To tune your radio into 90MHz, you need to set your 1/sqrt(LC)= 90MHz.

51. ( ) To tune your radio into 90MHz, you need to set your 1/sqrt(LC)= 2*3.14*90MHz, because =2f

RLC circuit

52. ( ) When a resistor is added to the ideal LC circuit, it is like added damping (air resistance or friction) to the spring mass system. It will make the gradually reduce the maximum current and voltage of each period. Some energy is converted into heat due to Joule heating I2 R.

53. ( ) When a resistor is added to the ideal LC circuit, the period and frequency will stay the same.

Chapter33.1. and 33.2

54. ( ) Our household electricity is AC (Alternating Current) instead of (Direct Current). AC circuits use an alternating voltage which can change between positive and negative values.

55. ( ) A typical AC voltage is the amplitude times a Sine-or-Cosine function of time. And the amplitude is the maximum voltage.

56. ( ) The angular frequency is 2 times frequency. And the period is 2 over the angular frequency.

57. ( ) The commercial power plants in the USA use a frequency of 60Hz, which corresponds to an angular frequency of 377 rad/s and a period of 1/377 second.

58.( ) When an AC voltage is applied to a resistor, the current is always equal to the maximum voltage over the resistance.

59. ( ) When an AC voltage is applied to a resistor, the current at any time is exactly equal to the instantaneous voltage over the resistance.

60. ( ) When an AC voltage is applied to a resistor, the current and the voltage vary together as a function of time and they are in phase, meaning that they reach the maximum, minimum and zero values and flip directions at the same time.

61. ( ) When an AC voltage is applied to a resistor, the current and the voltage vary together as a function of time and they are in phase, meaning that they reach the maximum, minimum and zero values and flip directions at the same time.

62. ( ) With the AC power source, the power consumed by a resistor is constant.

63. ( ) The average value of sin(t) during each period is zero. The average value of (sin(t))2 during each period is also zero.

64. ( ) The average value of sin(t) during each period is zero. The average value of (sin(t))2 during each period is also 1/2.

65. ( ) With the AC power source, the power consumed by a resistor is also changing as a function of time. p=i2 R =v2 /R is alternating as a function of the maximum power times (sin(t) )2 . Its average value during each period is half of the maximum power.

66. ( ) The maximum power a resistor consumes in an AC circuit is the equal to imax2 R = vmax2 /R.

67. ( ) The average power a resistor consumes in an AC circuit is the equal to imax2 R = vmax2 /R.

68. ( ) The average power a resistor consumes in an AC circuit is the equal to imax2 R/2 = vmax2 /2R.

69. ( ) The root mean square (rms) average of the AC current is equal to imax/2. The root mean square (rms) average of the AC voltage is equal to vmax/2.

70. ( ) The root mean square (rms) average of the AC current is equal to imax/sqrt(2). The root mean square (rms) average of the AC voltage is equal to vmax/sqrt(2). They are about 0.707 times of the maximum value.

71.( ) The average power a resistor consumes in an AC circuit is the equal to irms2 R = vrms2 /R.

72. ( ) The average power a resistor consumes in an AC circuit is the equal to irms2 R/2 = vrms2 /2R.

73. ( ) When we say that our AC power supply in the city is 120 volt, we mean that the amplitude voltage is 120 volt and the rms voltage is 120/sqrt(2)=120*0.707= 84.8volt. A1000 ohm bulb we use in the room will consume 84.82 /1000 watt of power.

74. ( ) When we say that our AC power supply in the city is 120 volt, we mean that the rms voltage is 120 volt and the amplitude voltage is 120*sqrt(2)=120*1.414=170 volt. A 1000 ohm bulb we use in the room will consume 1202 /1000 watt of power.

75. ( ) When we say that our AC power supply in the city is 120 volt, we mean that the rms voltage is 120 volt and the amplitude voltage is 120*sqrt(2)=120*1.414=170 volt. A 1000 ohm bulb we use in the room will consume 1702 /1000 watt of power.

Explanation / Answer

1 true as inductance oppose change in flux so it develop potential against the applied

2 true a = F/m so m large a will small

3 true as above

4 false inductance is property of internal circuit

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