Electrostatics
A positive charge has an electric field pointing ___.
Outward
Ohm's Law states that the current in a conductor is indirectly proportional to the _____.
Resistance
A stationary electron is placed in a uniform magnetic field. Will it experience a magnetic force? Why or why not?
No. Recall F = qv x B. No v, no force is applied.
According to ________ Law, a changing magnetic field induces an electromotive force in a circuit.
Faraday's Law
If cat fur is rubbed against a balloon (made of rubber), which of the objects gain electrons?
Balloon
What is the relationship between temperature (of a material) and its resistivity?
Directly Proportional
Using the right-hand rule, determine the direction of the magnetic field (when viewed from above) if the current flows upward.
Counterclockwise
According to Lenz’s Law, what is the direction of the induced current in a loop when the magnetic field through it is increasing upward?
The induced current flows to produce a downward magnetic field (opposite to the change).
If you enclose a charged object in a spherical surface and then change the shape of the surface into a cube, does the total electric flux through the surface change?
No, because the total electric flux only depends on the enclosed charge.
This fundamental law serves as the basis for Kirchhoff's laws.
Fundamental Law of Conservation of Charge
A straight wire carries a current of I=3.0 A. Find the magnitude of the magnetic field B at a distance of r=0.05 m from the wire.
1.2 x 10^(-5) T
A coil of 50 turns encloses an area of 0.02 m^2. The magnetic field through it increases uniformly from 0.10 T to 0.50 T in 0.20 s. Find the average induced emf.
2.0 V
If a positive test charge is moved towards a positive source charge, what happens to the electric potential energy?
Work is applied therefore electric potential energy is increased.
Due to their nature as being being able to repeat over certain periods of time, RC circuits are mostly used in what devices?
Timers
A proton moves at a constant speed in a uniform magnetic field but its path curves into a circle. Explain why the speed stays the same even though the direction changes.
Because the magnetic force is always perpendicular to the velocity (F=qv x B), it does no work and only changes direction (centripetal force) so the speed stays constant.
An inductor coil has 300 turns of copper wire that generates a magnetic flux of 2 Wb while passing a current of 4 A. Calculate the coil’s inductance.
150 H
If the electrical force of repulsion between two 1 C charges is 10 N, how far apart are they (in m)?
30 000 m
Explain the two Kirchhoff's Laws.
Kirchhoff's Current law states that the total loop passing through a node is zero, and Kirchhoff's Voltage law states that the total voltage in a closed circuit loop is zero.
Two long, parallel wires carry currents in opposite directions. Describe whether the wires attract or repel each other, and explain why using the concept of magnetic fields.
They repel. Opposite currents produce magnetic fields that make the Lorentz forces on each wire point away from the other.
A transformer works well with AC but not DC. Explain why. (Hint: a transformer contains a magnetic core, and AC source alternates the direction of current)
Transformers require a changing magnetic flux to induce voltage in the secondary coil; AC provides this by continuously changing direction and magnitude, while DC produces a constant flux (no continuous induction after the initial change).