Physical Science: Extension B (PEF)

Magnetic compasses work because Earth behaves as if there is a large bar magnet inside it, with the poles of the bar magnet located near Earth's geographic poles. Which of the following statements best explains why the North Pole of a compass needle points (approximately) toward the geographic North Pole of the Earth?

The South Pole of the imaginary large bar magnet inside the Earth lies close to the geographic North Pole.

Below are images of three positions of a compass near a bar magnet. The pointed end of the compass needle represents its North Pole. Only one of these three images shows the correct orientation of the compass needle, the other two are incorrect. Which image is correct? (If you wish, you can look at the movie again of the compass being moved around the magnet.)

B

Which one of the following statements is best supported by the evidence that you have seen in class and in this extension?

When two uncharged objects are rubbed together, if one of them acquires an electric charge of one sign (either + or -), the other object will always acquire the opposite charge.

In one of the movies you watched in the extension, a demonstrator rubbed a balloon on his hair. The balloon acquired a negative (-) charge. The evidence for this was that when the balloon was brought near the T-tape and B-tape, it attracted the + charged T-tape and repelled the - charged B-tape. When the balloon was brought near the demonstrator's hair, it attracted the hair. The picture to the left shows two pictures of the demonstrator's hair. The picture on the left shows the hair before the balloon was rubbed; the picture on the right shows the hair after the balloon was rubbed in the hair and moved away—but before it was brought close again. Examine the two pictures closely. Based on this evidence and the evidence described above, right after the balloon is rubbed, is the demonstrator's hair charged? If so, how is it charged? Hint: Consider that, after the balloon is rubbed against the hair, each strand of hair may be individually charged and can interact with adjacent hairs.

Yes, the hair is positively charged.