Physics Answers

1. A resistor with resistance R = 30 MΩ is connected in series with a capacitor with capacitance 3 μF. What is the

time constant?

2. Determine the equivalent (total) resistance for each of the following circuits below.

1. Why do lights on a car become dimmer when you start a car?

2. Some Christmas tree lights have a characteristic that when one light (filament) burns out, the lights throughout go

out too. However, burned-out lights go out in other series lights. Discuss the difference between these two sets of

lights.

1. Find the current density and drift velocity of free electrons when the particles travel on a copper conductor with a square cross-section of 1.0 mm on the side and carries a current of 40 A to a 5 hp electric meter and its density of 6.0 x 1028 electrons/m3

2. Suppose the resistance is 1.47 Ω at a temperature of 20°C. Find the resistance at 0 degree Celsius.

1. How would you expect the resistivity of a good insulator such as glass or polystyrene to vary with temperature?

2. A fuse is a device that is designed to break the circuit. It melts when the current exceeds its value. What

characteristics should the material have?

1. The potential energy of a certain system of two charges increases as the charges are moved farther apart. What does

this tell us about the sign of the charges? Why?

2. Show that volt per meter is the same as newton per coulomb.

3. A student said "electric potential is always proportional to potential energy; why bother with the concept of potential at

all? How would you respond?

1. A point charge q1 = +5.60 μC is at origin. How far should the second point charge of +8.10 μC be placed to have electric

potential energy of 0.900 J?

2. A point charge has a charge of 4.00 x 10-11 C. At what distance from the point charge is the electrical potential

(a) 8.0V?

(b) 16.0V?

a spaceship is designed with a rotating section to stimulate the effect of gravity for the astronauts. The internal radius of this section is 18.0 m. Calculate the tangential speed that the other wall must have in order for the astronauts to experience 1/2 g of artificial gravity when standing on it?