Module 11 Study Guide: Electricity and Magnetism

Question: The force between the south pole of a magnet and the north pole of another magnet is measured. If the distance between the poles is increased by a factor of 3, how does the new force compare to the old one? Is the force attractive or repulsive?

Answer: The magnetic force is inversely proportional to the square of the distance. If the distance is increased by a factor of 3, the force will decrease by a factor of 9 (3²). The force between a north pole and south pole is attractive.

Question: Two charged particles are placed 10 centimeters from each other and the resulting force is measured. The charge on object 1 is then doubled and the charge on object 2 is left the same. Also, the distance between the objects is reduced to 5 centimeters. How does the new force compare to the old force?

Answer: The force will be 8 times stronger. Doubling one charge doubles the force (×2), and reducing the distance by half increases the force by a factor of 4 (due to the inverse square relationship). So 2 × 4 = 8 times stronger.

Question: What causes the electromagnetic force?

Answer: The electromagnetic force is caused by the exchange of photons between charged particles.

Question: Given your answer to the previous question, why don't charged particles glow?

Answer: The photons exchanged in the electromagnetic force are virtual photons that cannot be directly observed. They are exchanged at the quantum level and do not produce visible light unless the charged particles are accelerated significantly.

Question: You have two wires. One is long and the other is short. Other than that, they are identical. Which has more resistance?

Answer: The longer wire has more resistance. Resistance is directly proportional to the length of the conductor.

Question: You have two wires. One is thin, and the other is very thick. When the same current is run through each wire, which will get hotter?

Answer: The thinner wire will get hotter. Thinner wires have higher resistance, which leads to more energy being converted to heat as current flows through them.

Question: In which circuit will the light bulb glow? (See diagrams in your textbook for open and closed circuits)

Answer: The light bulb will glow in the closed circuit where there is a complete path for electrons to flow from the negative terminal of the battery, through the bulb, and back to the positive terminal.

Question: Three lights are in a circuit. When one burns out, they all go out. When the burnt-out one is replaced with a good light, the other two lights work again. Are the lights wired in a parallel circuit or a series circuit?

Answer: The lights are wired in a series circuit. In a series circuit, all components share the same current path, so if one component fails (creating an open circuit), all components stop working.

Question: What is wrong with conventional current?

Answer: Conventional current flows from positive to negative, which is opposite to the actual flow of electrons (which move from negative to positive). This discrepancy exists because the convention was established before the direction of electron flow was understood.

Question: An electrical circuit uses a large voltage but a small current. Is the energy of each electron high or low? Are there many electrons flowing through the circuit, or are there few? Is the circuit dangerous?

Answer: With high voltage and low current, the energy of each electron is high (due to high voltage), but there are few electrons flowing (low current). The circuit could still be dangerous because high voltage can overcome the resistance of the human body and cause harm, even with low current.

Question: If it takes a flow of charged particles to make a magnet, where is the charged particle flow in a permanent magnet?

Answer: In a permanent magnet, the charged particle flow comes from the aligned electron spins within magnetic domains. The electrons in certain atoms have unpaired spins that create tiny magnetic fields, and when these are aligned in domains, they create the magnet's overall field.

Question: Is it possible to have a permanent magnet with only a north pole?

Answer: No, it is not possible to have a permanent magnet with only a north pole. Magnets always come as dipoles with both north and south poles. If you cut a magnet in half, each piece becomes a new magnet with both poles.

Question: Is it possible to make a magnet from something that is not a magnet?

Answer: Yes, ferromagnetic materials like iron can be magnetized by exposing them to a strong magnetic field or by running an electric current through a wire wrapped around them. This aligns their magnetic domains to create a magnet.

Question: If a material does not respond to a magnet, what can you conclude about the atoms in that material?

Answer: If a material does not respond to a magnet, its atoms either have fully paired electrons (with opposite spins that cancel each other's magnetic fields) or the arrangement of atoms prevents the alignment of magnetic domains. The material lacks unpaired electrons that could create magnetic fields.

Question: Suppose you have two wires lying side by side. In one wire, the current flows one way, and in the other, an equal amount of current flows the opposite way. Could you wrap those wires around a nail and make a magnet?

Answer: No, you could not make a magnet this way. The magnetic fields created by the two opposing currents would cancel each other out, resulting in no net magnetic field to magnetize the nail.

Question: What is the relationship between Earth's geographic north pole and magnetic north pole?

Answer: Earth's geographic north pole is not the same as its magnetic north pole. There is a difference of about 6 degrees latitude between them. What we call the magnetic north pole is actually a magnetic south pole (since it attracts the north pole of a compass magnet).

Question: Why does Earth have a magnetic field even though it doesn't have a huge bar magnet inside it?

Answer: Earth's magnetic field is believed to be generated by the movement of molten iron and nickel in the outer core. This flowing conductive material creates electric currents, which in turn produce the magnetic field through a process called the geodynamo effect.