Physics Lecture Review - Magnetism and Induction

50 practice flashcards in Question and Answer style generated from lecture notes on magnetism and electrical induction.

What is a Magnetic Field?

A region of space in which moving charged particles are subject to a magnetic force, caused by the interaction of its field with an existing Magnetic Field.

How is a Magnetic Field Line defined?

The path which a north pole would take when placed in a Magnetic Field.

In which direction do magnetic field lines go?

From north to south.

What is one method to map magnetic field lines around a magnet using iron filings?

Place iron filings on a piece of paper and then put the magnet on the paper; the filings will align to the field.

What is another method to map magnetic field lines around a magnet using a plotting compass?

Place a plotting compass in various positions around the magnet, mark the direction of the needle at each point, and connect them.

How is the strength of a Magnetic Field represented on a diagram?

By how close together the field lines are; the closer they are, the stronger the field.

Define Magnetic Flux Density.

The force per unit current per unit length on a current-carrying conductor placed in a Magnetic Field perpendicular to the field lines.

What is an alternative definition for Magnetic Flux Density?

Magnetic flux per unit area.

Why does a compass point towards the Earth's geographic North Pole?

The Earth's geographic north pole is actually its magnetic south pole, so the north pole of the compass needle aligns with the Earth's field, pointing to the magnetic south (which we call geographic north).

What rule helps determine the direction of the magnetic field around a current-carrying wire?

The right-hand thumb rule.

How is the right-hand thumb rule applied to a current-carrying wire?

Point your right thumb in the direction of the (conventional) current, and your fingers will curl in the direction of the magnetic field around the wire.

How is the north pole of a solenoid identified based on current direction?

Where the current circulates anticlockwise around the coil.

What does the magnetic field shape around a solenoid resemble?

A bar magnet.

Define the motor effect.

When a current-carrying conductor is placed within a Magnetic Field, it experiences a force perpendicular to both the current flow and the field lines.

What rule is used to determine the direction of the force in the motor effect?

Fleming's left-hand rule.

In Fleming's left-hand rule, what does the first finger represent?

Field lines.

In Fleming's left-hand rule, what does the thumb represent?

Motion (direction of the force).

State the formula for magnetic force (F) on a current-carrying conductor in a magnetic field.

F = BILsinθ.

What do the terms B, I, L, and θ represent in the formula F = BILsinθ?

B = Magnetic flux density (T), I = Current (A), L = Length of conductor in the field (m), θ = Angle between the field lines and the conductor.

What is the first step in an experiment to measure magnetic flux density using a horseshoe magnet and a digital balance?

Place a horseshoe magnet on a digital balance and zero it.

How is the force on the wire related to the change in mass on the balance in the flux density experiment?

Measure the extra mass on the balance (due to the downward force on the magnet by Newton's 3rd law) and calculate force using F = mg.

What is the formula for the magnetic force (F) on a moving charge (Q) at 90º to the field lines?

F = BQv.

How can the formula F = BQv be derived from F = BIL?

By substituting I = Q/t and L = vt into F = BIL, leading to F = BQvt/t, where 't' cancels out.

Explain why charged particles move in a circular orbit within a Magnetic Field.

The magnetic force is always perpendicular to the particle's velocity, causing centripetal acceleration and forcing it into a circular path.

How is the formula for the radius (r) of a circular orbit (r = mv / BQ) derived?

By equating the centripetal force (mv²/r) to the magnetic force (BQv) and rearranging.

According to r = mv / BQ, how does increasing the mass or velocity affect the radius of a charged particle's orbit?

Increasing mass or velocity will increase the radius.

According to r = mv / BQ, how does increasing the magnetic flux density or charge affect the radius of a charged particle's orbit?

Increasing flux density or charge will decrease the radius.

What is the primary purpose of a velocity selector?

To isolate particles of a specific velocity.

In a velocity selector, what condition must be met for particles to pass through undeflected?

The electric force must balance the magnetic force (BQv = EQ).

What formula for selected velocity can be derived from the principle of a velocity selector?

v = E/B.

Define Magnetic Flux.

The product of the magnetic flux density and the area perpendicular to the field lines.

What Greek letter represents Magnetic Flux?

Phi, ɸ.

What is the formula for Magnetic Flux (ɸ)?

ɸ = BAcosθ.

In the formula ɸ = BAcosθ, what does θ represent?

The angle between the normal to the coil and the field lines.

Define Magnetic Flux linkage.

The magnetic flux of an entire coil of wire, calculated as the product of the magnetic flux and the number of turns on the coil (Nɸ).

State Lenz's Law.

Induced emf is always in a direction so as to oppose the change that caused it.

How does Lenz's Law uphold the principle of the conservation of energy?

If induced emf aided the change, it would create electrical energy from nowhere, violating the conservation of energy, so it must oppose the change.

State Faraday's Law.

The induced emf in a circuit is proportional to the rate of change of flux linkage throughout the circuit.

What is a search coil used for?

To determine magnetic flux density by measuring the current induced when withdrawn from a Magnetic Field.

How is a search coil calibrated to measure magnetic flux density?

By placing it in a known Magnetic Field, withdrawing it, and calculating a constant of proportionality (k) from induced current and known B.

Describe the key structural component of a simple A.C. generator.

A rectangular coil which spins in a uniform Magnetic Field.

How does a simple A.C. generator produce alternating current?

The continuous change in flux linkage in the spinning coil induces an alternating current.

List two ways to increase the peak emf of an A.C. generator.

Increase the speed of rotation or increase the magnetic flux density of the field.

Name two other ways to increase the peak emf of an A.C. generator.

Increase the cross-sectional area of the coil or increase the number of turns on the coil.

What is the main function of a transformer?

To change the peak value of an alternating potential difference to a different value.

Describe the basic structural components of a simple transformer.

Two coils (primary and secondary) wrapped around a laminated iron ring.

How does an alternating current in the primary coil lead to an induced emf in the secondary coil of a transformer?

The alternating current induces an alternating Magnetic Field in the iron core, which then induces an alternating emf in the secondary coil.

What formula relates the potential difference and number of turns in the primary and secondary coils of a transformer?

Vs / Vp = Ns / Np.

For an ideal transformer, what formula relates the ratio of currents to the ratio of potential differences?

Ip / Is = Vs / Vp.

Why are step-up transformers crucial for the National Grid's long-distance electricity transmission?

They increase voltage and decrease current, significantly reducing energy lost as heat due to resistance in the transmission wires.