The Physical World I

Spring 2005
MWF 11:30

Instructor: Dr. Bruce Law, CW 327, Tel: 532-1618.

Home Work 21


R24.4. The rule for interaction between magnetic poles is similar to the rule for interaction between electrically charged particles, namely, like poles repel whereas unlike poles attract. For charged particles, like charges repel whereas unlike charges attract.

R24.5. Magnetic poles are very different than electric charges in that magnetic poles always come in pairs i.e. every N pole will always have an associated S pole. By contrast electric charges do not necessary come in pairs i.e. you can find a single positive or negative electric charge.

R24.7. A magnetic field is produced by moving electric charges eg. an electric current in a circuit or an electron moving around the nucleus of an atom.

R24.10. In an unmagnetized iron nail the magnetic domains are randomly oriented. In a magnetized iron nail, the magnetic domains point in the same direction.



E24.3. Attraction will occur because the magnet induces opposite polarity in a nearby piece of iron. North will induce south, and south will induce north. This is similar to electrical charge induction, where a balloon will stick to a wall whether the balloon is negatively or positively charged.

E24.21. Moving electrons are deflected from their paths by a magnetic field. A magnet held in front of a TV picture deflects the electron beam from its intended path and distorts the picture.

E24.23. Yes, it does. Since the magnet exerts a force on the wire, the wire, according to Newton`s third law, must exert an equal and opposite force on the magnet.



R25.3. The magnetic field must change with time in order to get electromagnetic induction in a closed loop.



E25.11. There is no fundamental difference between an electric motor and an electric generator. When mechanical energy is put into the device and electricity is produced, we call it a generator. When electrical energy is put in and it spins and does mechanical work, we call it a motor.