Electromagnetism MCQs | Physics MCQs

Using F = ILBsin(θ). F = (10 A) * (0.2 m) * (0.4 T) * sin(30°) = 2 * 0.4 * 0.5 = 0.4 N.

Factors like the number of turns, area, separation, and relative orientation of the coils determine how much of the flux from one coil links with the other.

The formula B = (μ₀I) / (2R) shows that the magnetic field is inversely proportional to the radius of the loop.

A step-down transformer is designed specifically to reduce the AC voltage.

The needle of a magnetic compass is a small magnet that will align itself with external magnetic field lines.

Using r = mv/qB. r = (1.67 x 10⁻²⁷ * 2 x 10⁶) / (1.6 x 10⁻¹⁹ * 0.1) ≈ 0.21 m or 21 cm.

At startup, speed is zero, so back EMF is zero. With no opposition to the supply voltage, the current (I = V/R) is at its maximum.

Ampere's Law provides a powerful method for calculating the magnetic field for current distributions with high degrees of symmetry, like long wires and solenoids.

Using B = µ₀nI. B = (4π x 10⁻⁷ T·m/A) * (1000 m⁻¹) * (2 A) = 8π x 10⁻⁴ T.

The radius of the circular path is r = mv/qB. Since the proton is much more massive, its radius will be larger. The direction of deflection will be opposite due to their opposite charges.

This action ensures that the current in the external circuit always flows in the same direction, converting the internally generated AC into a pulsating DC output.

This reflects the fact that there are no magnetic monopoles; every north pole is accompanied by a south pole.

Using F = ILBsin(θ), with L = 0.1 m and sin(90 degrees)=1, we get F = (5)(0.1)(0.2) = 0.1 N.

Where the lines are closer together, the magnetic field is stronger. Where they are farther apart, the field is weaker.

According to the Lorentz force equation, F = qvBsin(θ), if B=0, then F=0. No magnetic field means no magnetic force.

This rule correctly determines the direction of force on a positive charge moving in a magnetic field, where the thumb is velocity, fingers are the field, and the palm is the force.

A solenoid behaves like a bar magnet with a north and a south pole. It will align itself with the Earth's magnetic field lines.

The torsional constant represents the stiffness of the suspension. A smaller 'c' means the coil twists more easily for a given torque, leading to higher sensitivity.

Using the motional EMF formula E = BLv, we get E = (1)(1)(2) = 2 V.

The voltage ratio is equal to the turns ratio: Vs/Vp = Ns/Np. So, Vs = 120 * (200/100) = 240 V.

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

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'.

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

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.

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.

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

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).

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.

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.

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.

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

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.

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

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).

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.

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.

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

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.

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.

An AC generator uses slip rings to maintain a continuous connection, producing an alternating current. A DC generator uses a split-ring commutator to reverse the connection every half turn, producing a direct current.

The right-hand grip rule shows that the magnetic field lines form circles in a plane perpendicular to the wire.

The torque is given by τ = NIABsin(θ), where θ is the angle between the field and the normal. If θ = 0 degrees, sin(0 degrees)=0, so the torque is zero. The forces are pulling outwards, not causing rotation.

Using E = BLv. E = (0.2 T) * (0.5 m) * (4 m/s) = 0.4 V.

Faraday's Law of Induction, E = -N (dΦ/dt), directly relates the rate of change of magnetic flux to the induced EMF. For N=1, a rate of 1 Wb/s produces 1 V.

The energy stored is given by E = 1/2 LI². If I is doubled, the energy becomes 1/2 L(2I)² = 4(1/2 LI²), which is four times the original energy.

A metal detector uses a coil to generate a changing magnetic field. When a metal object is nearby, this field induces eddy currents in the metal. These currents, in turn, generate their own magnetic field that is detected by a second coil in the detector.

For the net force to be zero, the electric force (FE = qE) and the magnetic force (FB = qvB) must be equal in magnitude and point in opposite directions, so they cancel out.

A steady DC current creates a constant magnetic field and thus a constant magnetic flux. Transformers require a *changing* magnetic flux to induce a voltage in the secondary coil, according to Faraday's Law.

From the force equation on a wire, F=ILB, we can rearrange to B=F/IL. The units are Newtons / (Amperes * meters).

In a uniform magnetic field, the forces on opposite sides of the loop are equal in magnitude and opposite in direction, so they cancel out, resulting in zero net force.

The electron beam strikes a fluorescent screen, causing a single point to glow. This spot is then moved around by deflection plates to trace out a waveform.

For an ideal transformer, input power equals output power (VpIp = VsIs). So, Ip = (VsIs) / Vp = (12 V * 2.0 A) / 240 V = 0.1 A.

This is the definition of mutual induction, the principle behind transformers.

The output voltage of an ideal transformer depends on the turns ratio and the input voltage, not the frequency.

The induced EMF in a generator is given by E = NBAωsin(ωt). Since angular frequency ω = 2πf, the maximum EMF (E_max = NBAω) is directly proportional to the frequency. Doubling the frequency doubles the maximum EMF.

Paramagnetic materials have unpaired electrons that align with an external magnetic field, causing a weak attraction.

Using F = qvBsin(θ), with sin(90°)=1. F = (2 x 10⁻⁶ C) * (3 x 10⁶ m/s) * (0.5 T) = 3.0 N.

The soft iron core concentrates the magnetic field lines, making the field stronger. When shaped cylindrically, it also ensures the field is radial, meaning the torque is proportional to the current for a wider range of deflection.

This energy loss is represented by the area of the material's hysteresis loop. It is the energy required to re-orient the magnetic domains in the core with each AC cycle.

Cutting a magnet simply creates two smaller magnets, each complete with its own north and south pole.

The force is given by F=qvBsin(θ). The sine function is maximum (value of 1) when the angle θ is 90 degrees.

This condition ensures that the magnetic field inside is strong and uniform, and the field outside is negligible, which is the definition of an ideal solenoid.

Due to the commutator action, the output voltage rises from zero to a maximum and back to zero, but always with the same polarity. This creates a pulsating DC.

Using E = 1/2 LI². E = 0.5 * (80 x 10⁻³ H) * (5 A)² = 0.5 * 0.08 * 25 = 1.0 J.

Similar to resistors in series, inductances in series add up (assuming no mutual inductance).

This branch of physics deals with the phenomena and properties of stationary or slow-moving electric charges with no acceleration.

The radius of the circular path is given by r = mv/qB. Therefore, for a given velocity, field, and charge, the radius is directly proportional to the mass. This allows separation of isotopes.

Using Φ = BAcos(θ). Since the field is perpendicular to the surface, the angle θ with the normal is 0°, and cos(0°)=1. So, Φ = (0.5 T) * (0.2 m²) = 0.1 Wb.

Lenz's Law is specifically used to determine the direction of the induced current by stating that it will flow in a direction that opposes the change in flux that created it.