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| 1 | |
A room has its walls aligned accurately with respect to north, south, east, and west. The north wall has an area of 15 m2, the east wall has an area of 12 m2, and the floor's area is 35 m2. At the site the Earth's magnetic field has a value of 0.60 G and is directed 50° below the horizontal and 7.0° east of north. Find the fluxes through the north wall, the east wall, and the floor. |
| | A) | (a) 0.57 mWb, (b) 46 µWb, (c) 1.6 mWb |
| | B) | (a) 0.90 mWb, (b) 56 µWb, (c) 0.57 mWb |
| | C) | (a) 0.69 mWb, (b) 88 µWb, (c) 12.1 mWb |
| | D) | (a) 5.7 Wb, (b) 46 µWb, (c) 16 Wb |
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| 2 | |
A flat coil with radius 8.0 mm has 50 loops of wire. It is placed in a magnetic field B=0.30 T in such a way that the maximum flux goes through it. Later, it is rotated in 0.020 s to a position such that no flux goes through it. Find the average emf induced between the terminals of the coil. |
| | A) | 0.15 V |
| | B) | 15 mV |
| | C) | 18.8 V |
| | D) | 3.0 mV |
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| 3 | |
A train is moving directly south with a speed of 10 m\s. If the downward vertical component of the Earth's magnetic field is 0.54 G, compute the magnitude and direction of the emf induced in a rail car axle 1.2 m long. |
| | A) | 6.5 V from WEST to EAST |
| | B) | 0.65 mV from WEST to EAST |
| | C) | 0.065 mV from WEST to EAST |
| | D) | 450 mV from WEST to EAST |
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| 4 | |
Determine the separate effects on the induced emf of a generator if (a) the flux per pole is doubled, and (b) the speed of the armature is doubled. |
| | A) | (a) halved, (b) halved |
| | B) | (a) quadrupled, (b) quadrupled |
| | C) | (a) doubled, (b) doubled |
| | D) | (a) no change, (b) no change |
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| 5 | |
A generator has an armature with 500 loops, which cut a flux of 8.00 mWb during each rotation. Compute the back emf it develops when run as a motor at 1500 rpm. |
| | A) | 100 V |
| | B) | 100 kV |
| | C) | 6.0 kV |
| | D) | 0.2 V |
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| 6 | |
A shunt motor is connected to a 110-V line. When the armature generates a back emf of 104 V, the armature current is 15 A. Compute the armature resistance. |
| | A) | 6.9 ohm |
| | B) | 90 ohm |
| | C) | 2.5 ohm |
| | D) | 0.40 ohm |
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| 7 | |
A step-up transformer is used on a 110-V line and supplies a load with 2.0 A. The ratio of the primary and secondary wingdings is 1:25. Determine the secondary voltage, the primary current, and the power output. Assume a resistive load and 100 percent efficiency. |
| | A) | (a) 4.40 V, (b) 0.08 A, (c) 0.22 kW |
| | B) | (a) 2.75 kV, (b) 50 A, (c) 5.5 kW |
| | C) | (a) 6.88 kV, (b) 1350 A, (c) 0.14 kW |
| | D) | (a) 0.23 V, (b) 12.5 A, (c) 0.61 MW |
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| 8 | |
An emf of 8.0 V is induced in a coil when the current in it changes at the rate of 32 A/s. Compute the inductance of the coil. |
| | A) | 4.0 mH |
| | B) | 250 mH |
| | C) | 256 H |
| | D) | 24 H |
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| 9 | |
A steady current of 2.5 A creates a flux of 1.4 x 10-4 Wb in a coil of 500 turns. What is the inductance of the coil? |
| | A) | 560 mH |
| | B) | 250 mH |
| | C) | 12.5 mH |
| | D) | 11.2 nH |
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| 10 | |
A coil of 0.48 H carries a current of 5 A. Compute the energy stored in it. |
| | A) | 12 J |
| | B) | 6 J |
| | C) | 1.2 J |
| | D) | 0.6 J |
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