Electromagnetism Test. 4

When the plane of the coil is horizontal (moving parallel to the field), the sides of the coil are cutting the flux at the maximum rate.

As the magnet falls, it induces eddy currents in the copper tube. According to Lenz's law, these currents create a magnetic field that opposes the magnet's motion, resulting in a braking force and an acceleration less than g.

A transformer changes voltage and current, but for an ideal transformer, the power (P=VI) remains constant. A step-up transformer increases voltage but decreases current.

An ammeter must be in series to measure the flow of current through it. A voltmeter must be in parallel to measure the potential difference across a component.

The magnetic force is always perpendicular to the velocity of the charge. Since work done is W = Fdcos(θ) and θ = 90 degrees, the work done is zero. The magnetic field only changes the direction of the charge, not its speed or kinetic energy.

Using the right-hand rule for a positive charge gives a force to the right. Since an electron is negative, the force is in the opposite direction, to the left.

In ferromagnetic materials, atoms group into domains where their magnetic moments are aligned, creating a strong local magnetic field.

A transformer relies on a changing current in one coil (the primary) inducing a changing magnetic flux and thus an EMF in a nearby second coil (the secondary).

The rotation of the motor's coil in the magnetic field induces an EMF (back EMF) that opposes the supply voltage, thus creating a 'back current'.

The time period T = 2πr / v and the radius r = mv / qB. Substituting for r gives T = 2πm / qB. The velocity 'v' cancels out.

The resonant frequency ω = 1/sqrt(LC). To keep ω constant, if L is doubled, C must be halved so that the product LC remains the same.

Resistance affects the magnitude of the induced *current* (I = E/R), but not the induced EMF (E) itself.

The potential difference across the galvanometer (Ig * G) must equal the potential difference across the shunt (Is * S = (I - Ig) * S). Rearranging for S gives the correct formula.

The grid is made negative with respect to the cathode. By varying this negative potential, it controls the number of electrons passing through, thus controlling the brightness of the spot on the screen.

The insulating layers between the laminations break up the paths of induced currents (eddy currents), significantly reducing heat loss.

This is the defined value for the permeability of free space, fundamental to electromagnetism.

Using the right-hand grip rule, the field from the first wire and the field from the second wire are in the same direction at the midpoint, so they add together. Since the point is midway, the total field is double the field from one wire.

Since radius r is proportional to velocity v, and velocity is proportional to the square root of kinetic energy (v is proportional to sqrt(K)), doubling K will multiply the radius by sqrt(2).

Using E = -L (ΔI / Δt), we have 3 = -L * ((2-5) / 0.1) = -L * (-3 / 0.1) = L * (30). So, L = 3/30 = 0.1 H.

From the formula E = -L (ΔI / Δt), we can rearrange to L = -E (Δt / ΔI), giving units of (Volt)(second)/Ampere.