Deck 15: Electromagnetic Oscillations and Alternating Current

Question 1

The electrical analog of a spring constant k is:

A) L
B) 1/L
C) C
D) 1/C
E) R

Answer 1

1/C

Question 2

A 150-g block on the end of a spring with a spring constant of 35 N/m is pulled aside 25 cm and released from rest. In the electrical analog the initial charge on the capacitor is:

A) 0.15 C
B) 6.67 C
C) 0.025 C
D) 40 C
E) 35 C

Answer 2

0.025 C

Question 3

In an oscillating LC circuit, the total stored energy is U and the maximum charge on the capacitor is Q.When the charge on the capacitor is Q/2, the energy stored in the inductor is:

A) U/2
B) U/4
C) (4/3)U
D) 3U/2
E) 3U/4

Answer 3

3U/4

Question 4

The rapid exponential decay in just a few cycles of the charge on the plates of capacitor in an RLC circuit might due to:

A) a large inductance
B) a large capacitance
C) a small capacitance
D) a large resistance
E) a small resistance

Question 5

In a purely resistive circuit the current:

A) leads the voltage by 1/4 cycle
B) leads the voltage by 1/2 cycle
C) lags the voltage by 1/4 cycle
D) lags the voltage by 1/2 cycle
E) is in phase with the voltage

Question 6

In a purely inductive circuit, the current lags the voltage by:

A) 0
B) one-fourth of a cycle
C) one-half of a cycle
D) three-fourths of a cycle
E) one cycle

Question 7

A 45-mH inductor is connected to an ac source of emf with a frequency of 400 Hz and a maximum emf of 20 V. The maximum current is:

A) 0
B) 0.18 A
C) 1.1 A
D) 360 A
E) 2300 A

Question 8

An RL series circuit is connected to an ac generator with a maximum emf of 20 V. If the maximum potential difference across the resistor is 16 V, then the maximum potential difference across the inductor is:

A) 2 V
B) 4 V
C) 12 V
D) 25.6 V
E) 36 V

Question 9

The impedance of an RLC series circuit is definitely increased if:

A) C decreases
B) L increases
C) L decreases
D) R increases
E) R decreases

Question 10

When the frequency of the oscillator in a series RLC circuit is doubled:

A) the capacitive reactance is doubled
B) the capacitive reactance is halved
C) the impedance is doubled
D) the current amplitude is doubled
E) the current amplitude is halved

Question 11

The rms value of an ac current is:

A) its peak value
B) its average value
C) that steady current that produces the same rate of heating in a resistor
D) that steady current that will charge a battery at the same rate
E) zero

Question 12

A sinusoidal voltage V(t) has an rms value of 100 V. Its maximum value is:

A) 100 V
B) 707 V
C) 70.7 V
D) 141 V
E) 200 V

Question 13

The units of the power factor are:

A) ohm
B) watt
C) radian
D) ohm^1/2
E) none of these

Question 14

A step-down transformer is used to:

A) increase the power
B) decrease the power
C) increase the voltage
D) decrease the voltage
E) change ac to dc

Question 15

The core of a transformer is made in a laminated form to:

A) facilitate easy assembly
B) reduce i²R losses in the coils
C) increase the magnetic flux
D) save weight
E) prevent eddy currents

Question 16

A generator supplies 100 V to the primary coil of a transformer. The primary has 50 turns and the secondary has 500 turns.The secondary voltage is:

A) 1000 V
B) 500 V
C) 250 V
D) 100 V
E) 10 V

Question 17

In an ideal 1:8 step-down transformer, the primary power is 10 kW and the secondary current is 25 A. The primary voltage is:

A) 25,600 V
B) 3200 V
C) 400 V
D) 50 V
E) 6.25 V