Q3. The magnetic field lines make concentric circles around the wire with the arrows pointing counter-clockwise (according to the right-hand rule).
Q7. If both bars are magnets you will have attraction when opposite poles are close and repulsion when similar poles are close. If you try all the combinations of placing ends close together, you should get attraction half of the time and repulsion half of the time. If only one of the bars is a magnet, it will always induce an opposite pole in the end of the other bar and attraction will always occur. This is what is observed so both bars cannot be magnets.
Q18. See table below
| WHICH CHARGE ? | DIRECTION OF "B" | DIRECTION OF "F" |
| + charge on upper left | Up out of the page | Toward the wire |
| - charge on upper right | Up out of page | To the left parallel to the wire |
| - charge on lower left | Down into page | Toward the wire |
| + charge on lower right | Down into page | To the left parallel to the wire |
Q26. Positive charge carriers move through the semiconductor in the same direction as the current, from left to right. The magnetic force they would experience, according to the right-hand rule, is toward "a." If positive charge collects at side "a," this becomes the high voltage side of the sample. Negative charge carriers move through the sample in a direction opposite to the current. They would experience a force directed toward "a" according to the right-hand rule just as occurs with positive charge carriers. If negative charge collects at side "a," this becomes the low voltage side of the sample. Since side "a" is found to be the high voltage side, positive charge carriers must move through the sample.
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