# Ch 25 physics

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1. Disconnect a small-voltage battery from a coil of many loops of wire and a large voltage is produced by
the large collapse in the magnetic field
2. Metal detectors, like the ones used at airports, are activated by
electromagnetic induction
3. Four amperes of current exist in the primary coil of a transformer. The voltage across the primary coil is 110 V. What is the power output of the secondary of the secondary coil?
440 W
4. A transformer actually transforms
voltage
5. A device that transforms mechanical energy into electrical energy is a
generator
6. Neon signs require about 12,000 volts to operate. If the circuit uses a 120-volt power source, the ratio of primary to secondary turns on teh transformer should be
1:100
7. An electric motor and electric generator are
• very similar devices.
• Difference is to switch input and output (electric energy and mechanical energy)
8. electric power can be transmitted from one place to another without the need for connecting wires in between. The statement is
• true.
• e.g. transformer in-between. Sun light. Microwave.
9. If a magnet is pushed into a coil, voltage is induced across the coil. If the same magnet is pushed into a coil with twice the number of loops
• twice as much voltage is induced.
10. Voltage can be induced in a wire by
• moving the wire near a magnet
• &
• moving a magnet near the wire
• &
• hanging the current in a nearby wire
11. The primary of a transformer is the coil connected to
the power source
12. A device that transforms mechanical energy into electrical energy is a
generator
13. Compared to the primary voltage, the secondary voltage may be
larger, smaller, or the same
14. The magnetic field strength inside a current-carrying coil will be greater if the coil encloses a
rod of iron
15. The voltage across the input terminals of a transformer is 110 V. The primary has 50 loops and the secondary has 25 loops. The voltage the transformer puts out is
55 V
16. A step-up transformer has a ratio of one to ten. Neglecting slight losses, if 100 W of power go into the primary coil, the power coming from the secondary coil is
• 100 W.
• Transformer only affect voltage output, not power or energy output.
17. Rapid change of a magnetic field induces
• an electric field.
18. Power is transmitted at high voltage because the corresponding current in the wires is
low so that overheating of the wires is minimized. P = IV. For same P, higher V means lower I. lower I means lower loss.
19. A certain transformer doubles input voltage. If the primary coil has 10 A of current, the secondary current is
• 5 A.
• P = IV. If V is stepped up, I will be stepped down. P is constant.
20. The output power of a transformer is
equal to the input power
21. A step-up transformer increases; energy or power?
neither of these
22. If the primary of a transformer were connected to a dc-power source, the transformer would have a voltage output
only while being connected or disconnected.
23. A device that transforms electrical energy to mechanical energy is a
motor
24. Thrust a magnet into a coil of wire and the coil
becomes electromagnetic. has a current in it

both of these
25. The principal advantage of ac power over dc power is that
• ac voltage can be transformed via conventional transformers.
• Transformer is based on Faraday's law and only works for AC voltage.

 Author: k33m ID: 219451 Card Set: Ch 25 physics Updated: 2013-05-13 21:20:38 Tags: physics Folders: Description: practice for exam Show Answers: