Circuits and magnets quiz

Define electric current in terms of charged particle flow

Current is the flow of charged particles, such as electrons in a wire or ions in a solution.

What unit is current measured in, and what device measures it?

Measured in amperes (A) with an ammeter.

Why must an ammeter be connected in series, not parallel?

Because it must measure the total flow of charge through the circuit, which only occurs when connected in series.

Explain the difference between conventional current and electron flow.

Conventional current flows from positive to negative; electrons actually flow from negative to positive.

In a circuit with a battery and a resistor, describe the path of current flow.

From the positive terminal of the battery, through the resistor, then back to the negative terminal.

What is voltage and why is it sometimes called electromotive force?

Voltage is the potential difference that drives current; it’s called electromotive force because it pushes charges through the circuit.

How is voltage measured in a circuit?

With a voltmeter, connected in parallel across a component.

State and explain Ohm’s Law.

Ohm’s Law: V = IR. Voltage is equal to current multiplied by resistance.

A 12V battery is connected across a 4Ω resistor. Calculate the current.

I = V/R = 12 ÷ 4 = 3A.

A circuit has a current of 2A and resistance of 10Ω. Calculate the voltage.

V = IR = 2 × 10 = 20V.

Define resistance and state its unit.

Resistance is opposition to current flow; measured in ohms (Ω).

Compare resistance of insulators and conductors with examples.

Conductors: low resistance (e.g., copper, aluminium, graphite).
Insulators: high resistance (e.g., rubber, glass, plastic).

A lamp has resistance of 8Ω and current of 1.5A. Calculate the voltage.

V = IR = 1.5 × 8 = 12V.

A resistor has 12V across it and current of 4A. Find its resistance.

R = V/I = 12 ÷ 4 = 3Ω.

In a parallel circuit, what happens to voltage across each branch?

Each branch has the same voltage as the supply.

In a parallel circuit, how does total current relate to branch currents?

Total current = sum of currents in each branch.

What happens if one branch fails in a parallel circuit?

Other branches continue to work.

Three resistors (2Ω, 3Ω, 6Ω) are in parallel with a 12V supply. Find current in each and total.

I₁ = V/R = 12 ÷ 2 = 6A

I₂ = 12 ÷ 3 = 4A

I₃ = 12 ÷ 6 = 2A

Total = 6 + 4 + 2 = 12A

What makes a material a conductor? Examples.

Presence of free-moving charged particles (electrons/ions). Examples: copper, aluminium, graphite.

What makes a material an insulator? Examples.

Lack of free-moving charged particles. Examples: wood, rubber, glass.

Why copper for wires and rubber for coatings?

Copper conducts electricity well (low resistance), rubber prevents shocks (high resistance).

Why does saltwater conduct but pure water doesn’t?

Saltwater has free ions that carry current; pure water has very few charged particles.

Difference between a cell and a battery?

A cell is a single unit; a battery is multiple cells connected together.

How does a battery convert energy?

Converts chemical potential energy into electrical energy via chemical reactions.

Why does voltage decrease as a battery is used?

Because chemical reactants are gradually used up.

What is the nominal voltage of an AA battery?

1.5V

Which materials can be made into permanent magnets?

Iron, steel, cobalt, nickel.

Rule for attraction/repulsion?

Like poles repel, unlike poles attract.

Why does a compass needle point north?

Because Earth’s magnetic field attracts the needle towards the magnetic south pole near the geographic North.

Why is Earth’s magnetic north actually a south pole?

Magnetic field lines go from north to south, so the geographic North attracts the north-seeking pole of a compass — meaning it is a magnetic south pole.

Two uses of Earth’s magnetic field?

Navigation (compasses), protecting Earth from solar wind.

How is an electromagnet created?

By running electric current through a coil of wire.

Three ways to increase electromagnet strength?

Increase current, increase number of coils, add a ferromagnetic core (e.g., iron nail).

What happens when a magnet is moved past a wire? Name the law.

A current is induced; described by Faraday’s Law of Induction.

Three real-life uses of electromagnets.

Electric bells, relays, magnetic locks.

Why are electromagnets preferred over permanent magnets in machines?

Their magnetism can be turned on/off and strength controlled.