electricity and magnetism chapter 17 – intro to electricity chapter 18 – electromagnetism

Electricity and MagnetismElectricity and MagnetismChapter 17 – Intro to ElectricityChapter 18 – Electromagnetism

1. Like charges _____ each other, unlike charges ____ each other. (p. 423)

1. Like charges repel each other, unlike charges attract each other. (p. 423)

2. What are the 3 ways that an object can become charged? Explain each one.

a. Friction: by rubbing 2 objects together, electrons move from the surface of 1 object to the other resulting in an imbalance of charges.

b. Conduction: electrons are transferred from one object to another by direct contact.

c. Induction: Charges in an uncharged object are rearranged without direct contact.

3. What is static electricity? (p. 427)

The buildup of electric charges on an object.

4. How (and why) do lightning rods protect buildings from lightning? (p. 429)

Lightning rods direct the lightning down

into the earth where the charges are dispersed without harm.

5. How is current electricity different from an electric discharge?

Electric current is the continuous movement of electrons . Electric discharge is the loss of static electricity as charges move off an object.

6. Order the following from the least resistance to the most resistance: a thick, short wire, a thick long wire, a thin long wire, and a thin short wire. (p. 436)

1. Thick short 2. Thin short OR 3. Thick long 4. Thin long

1. Thick short 2. Thick long OR 3. Thin short 4. Thin long

WHY?

7. Do the “Math Break on page 437 and show your work.

Use R = V / I and I = V / R Remember, V = voltage in volts (V) I = current in amperes (A)

1. R = 10V x 0.5 A = 20 Ω R = resistance in

ohms (Ω)2. I = 36V/4 Ω = 9 A

8. What is a circuit, and explain the difference between an open and closed circuit? (p. 440 – 441)

Circuit: a pathway for electrons to travel;

Closed Circuit: pathway is continuous and the electrons will travel incessantly through the circuit;

Open Circuit: pathway is not continuous and electrons will not travel through this circuit

9. Draw a series and parallel circuit with a power source, switch and 3 light bulbs. Explain what happens when a light bulb breaks in each circuit? (p. 442 – 443)

Series CircuitSeries Circuit

Series: When a bulb goes out in a series circuit, the entire circuit goes out. The burned out bulb acts like an open switch.

Parallel CircuitParallel Circuit

Parallel: In a parallel circuit, if a bulb burns out, the other bulbs continue to burn because each bulb has its own independent circuit or source of electrical current.

10. What does the switch do in the previous drawings?

The switch, if open, stops the continuous flow of electrons. If closed, it allows the continuous flow of electrons.

11. How do circuit breakers and fuses protect circuits?

Fuses contain a thin strip of metal through which charges flow. If the current is too high, the metal in the fuse warms up and melts, creating a break or gap in the circuit.

A circuit breaker is a switch that automatically opens if the current in the circuit is too high. Open circuit breakers can be closed easily by flipping a switch inside the breaker box once the problem has been corrected.

12. How does a magnet impact a compass? (p. 455)

Causes the compass needle to point North

13. Like poles of a magnet ____ each other. Unlike poles of a magnet _____ each other? (p. 455)

Like poles of a magnet repel each other. Unlike poles of a magnet attract each other? (p. 455)

14. Explain what happens when you cut a magnet in half (p. 458)

You get 2 smaller magnets. Both have a N and S pole.

15. An electric current induces a ______ field. (p. 462 – 463)

An electric current induces a magnetic field. (p. 462 – 463)

16. How do you turn on and off an electromagnet?

By introducing an electric current through a solenoid or removing the electric current.

17. How do you make an electromagnet more powerful? (p. 464)

By adding more loops to the solenoid.

18. Explain how an electric motor works? (p. 466)

An electric current in the armature causes the magnet to exert a force on the armature. Because of the direction of the current on either side of the armature, the magnet pulls up on one side and down on the other, causing the armature to rotate. As the armature rotates, the commutator causes the electric current in the coil to change directions. When the electric current is reversed, the side of the coil that was pulled up is pulled down, and the side that was pulled down is pulled up. This keeps the armature rotating.

19. What is electromagnetic induction and how is it used to generate electricity? (p. 469 – 471)

An electric current is produced by a changing magnetic field. For example, when a battery is connected or disconnected, an electric current is produced.

20. How are an electric motor and generator similar?

They both have a rotating armature between the poles of a magnet creating an electric current. They are basically the same machine acting in reverse. An electric motor converts electrical energy into kinetic energy and a generator converts kinetic energy into electrical energy.

21. Explain how you would use a transformer to increase and decrease the voltage. (p 472)

There are 2 types of transformers: Step-up (used to increase the amount of voltage) and Step-down (used to decrease the amount of voltage). Step-up transformers are used as electricity is leaving the power station. This is to compensate for the loss of electricity over a long journey to your home. When the electricity arrives at your home, it travels through a Step-down transformer so that the electricity is at a usable level inside your home.

22. When electricity enters your home from the power lines it ________

C. involves the flow of negatively charged particles.

23. Static electricity is different from current electricity because static electricity occurs when _______

C. negative charges move to an object because of friction or induction.

24. Lightning occurs when _____A. negative charges built up in the clouds must be discharged to positively charged areas or objects.

25. Which diagram shows the path of electrical current in a circuit?

26. What do the three objects above have in common?

D. Electrical charges move easily through these conductors.

27. If Bulb A burns out in the circuit above, what would happen?

B. Bulbs B and C would NOT light because this is a series circuit.

28. Two magnets of equal strength are placed end to end. How would you place the two magnets so that they have the strongest attractive force toward each other?

29. A coiled wire is connected to the positive and negative poles of a battery. The current moving through the wire produces an electric field. When you move the compass to opposite ends of the coiled wire, why does the compass show an opposite direction for North?

C. The electric field produced around the coiled wire induced a magnetic field.

30. Why is alternating current typically used to deliver electricity to your school or home?

C. Power companies can easily transmit high voltage AC current and reduce it before it enters a building.

31. Which diagram represents the best transformer to deliver electricity from the power lines to the house?

D A step-down transformer lower high voltage current to a lower voltage for use in your home.