QCAA Physics Electromagnetism

This describes the domain for calculating magnetic flux, which is the integral of the magnetic field over an area, rather than defining the field itself.

This is a generic definition that could apply to gravitational or electric fields; it fails to specify that the force is magnetic or that it acts on magnets and moving charges.

This is the definition of an electric field, which exerts forces on stationary or moving electric charges, whereas magnetic fields specifically affect moving charges or magnetic materials.

Incorrect. The explanation of atomic emission spectra was developed later by Niels Bohr and other quantum physicists using quantum mechanics, not by Maxwell.

Incorrect. Maxwell's work firmly established the wave model of light; experimental support for the particle model came later from Einstein's explanation of the photoelectric effect.

Incorrect. Maxwell provided the theoretical framework for electromagnetic waves, but experimental confirmation of invisible light like infrared and radio waves was achieved by scientists like Herschel and Hertz.

This value is too small. The calculated magnetic field strength is approximately $0.015 \text{ T}$, which is two orders of magnitude larger than $10^{-4} \text{ T}$.

This value is significantly larger than the actual magnetic field. The calculation yields $B \approx 0.015 \text{ T}$, whereas $10^2 \text{ T}$ represents an extremely strong magnetic field not supported by the data.

This value is far too large. The calculated field strength is approximately $1.5 \times 10^{-2} \text{ T}$, which is six orders of magnitude smaller than $10^4 \text{ T}$.

This rotation speed is too slow. Using the formula $\varepsilon_{avg} = 4NBAf$, a frequency of $1 \text{ rev/s}$ would only produce an average EMF of $0.48 \text{ V}$.

This value is insufficient. Substituting $f=3$ into the average EMF equation yields approximately $1.44 \text{ V}$, which is less than the required $6 \text{ V}$.

This frequency is too high. At $50 \text{ rev/s}$, the generated average EMF would be $24 \text{ V}$, far exceeding the required $6 \text{ V}$.

The change in electrical potential energy per unit charge between two points defines electric potential difference (voltage), not electric field strength.

The rate at which charged particles pass a specific point defines electric current ($I = Q/t$), not electric field strength.

This describes electric charge, which is the property of matter that causes it to experience a force, whereas electric field strength describes the field itself.

Decreasing wire thickness increases electrical resistance, which would reduce the current $I$ (for a fixed voltage) and consequently decrease the magnetic field strength.

The magnetic field strength $B = \mu_0 \frac{N}{L} I$ is inversely proportional to the length $L$; increasing the length while keeping the number of turns constant decreases the turn density, weakening the field.

Alternating current produces a magnetic field that fluctuates in magnitude and direction, and inductive reactance often reduces the current compared to DC, which would not increase the field strength.

This is the value for the electric potential ($V = \frac{kQ}{r}$), not the electric field strength ($E = \frac{kQ}{r^2}$).

This value represents the electric potential calculated incorrectly by using the mass number (4) instead of the atomic number (2) for the charge.

This result comes from incorrectly using the mass number (4) instead of the atomic number (2) to calculate the total charge ($Q = 4e$).

Electric charge is a fundamental conserved property and does not decrease due to motion or the presence of a magnetic field.

The magnitude of an electric charge is invariant; it does not increase regardless of its speed or the external fields applied.

The magnetic force is the result of a cross product ($\\vec{F} = q\\vec{v} \\times \\vec{B}$), which produces a vector perpendicular to the magnetic field, not parallel to it.

While transformers are indeed used to step up the voltage, this explains how high voltages are achieved, not why they are beneficial for long-distance transmission.

While high voltages are used to transmit large amounts of power, the fundamental reason for stepping up the voltage is to minimize power loss during transmission, not just to increase capacity.

The resistance of a transmission line is determined by its physical properties (material, length, and cross-sectional area), not by the voltage applied to it.

This describes electric field strength ($E$), which is the force exerted per unit charge at a specific location, not the energy.

This describes electric potential difference (voltage), which is the difference in electric potential energy per unit charge between two points.

This is the specific definition of an electron-volt (eV), a unit of energy, rather than the general definition of electrical potential energy.

The magnetic force depends on velocity ($F_B = qvB$), so doubling the velocity doubles the magnetic force. This unbalances it with the constant electric force, resulting in a non-zero net force and acceleration.

The initial net force changes the proton's velocity vector. Since the magnetic force depends on this changing velocity, the net force and acceleration cannot remain constant.

As the proton's velocity changes in both magnitude and direction relative to the magnetic field, the magnitude of the magnetic force (and thus the net acceleration) will also change, not just its direction.