# Solve problems involving Ohm’s Law and electric circuits

**Week 3 Assignment**

Please solve the following problems. **You must show all work for full/partial credit.** Must be submitted in a word document.

**Question 1 : **

If a charge particle moves in a straight line and there are no other forces on it, except possibly from a magnetic field, can you say with certainty that no magnetic field is present? Explain.

**Question 2 : **

In a velocity sector, the uniform magnetic field of 1.5 T is produced by a large magnet. Two parallel plates with a separation of 1.5 cm produce the perpendicular electric field. What voltage should be applied across the plates so that:

- A singly ionized ion traveling 8.0×10⁴ m/s will pass through undeflected
- A double ionized ion traveling at the same speed will pass through undeflected

**Question 3 **

A horizontal magnetic field of 1.0×10⁻⁴T is at an angle of 30° to the direction of the current in a straight wire 75 cm long. If the wire carries a current of 15 A, what is the magnitude of the force on the wire?

**Question 4 **

An electron travels at a speed of 2.0×10⁻⁴ m/s through a uniform magnetic field of strength 1.2×10⁻³T. What is the magnitude of the magnetic force on the electron if its velocity and the magnetic field:

- Are perpendicular
- Make an angle of 45°
- Are parallel
- Are exactly opposite

**Question 5 **

A square loop of wire with sides of length 40 cm is in a uniform magnetic field perpendicular to its area. If the field’s strength is 100 mT and it decays to zero in 0.010 seconds:

- What is the magnitude of the average emf induced in the loop?
- What happens to the emf if the side lengths are reduce by a factor of ½?

**Question 6 **

The armature of an ac generator has 100 turns. Each turn is a rectangular loop measuring 8.0 cm by 12 cm. The generator has a sinusoidal voltage output with an amplitude of 24 V. If the magnetic field of the generator is 250 mT:

- With what frequency does the armature turn?
- If you double the B and cut w in half, how does this affect the amplitude?

**Question 7 **

An ac generator supplies 20 A at 440 V to a 10,000 V power line. If the step up transformer has 150 turns in its primary coil, how many turns are in the secondary coil?