AQA A-Level Physics 5.1 Current Electricity Flashcards

Flashcards covering key concepts in current electricity for AQA A-Level Physics.

What is electric current and its units?

The rate of flow of charge, measured in amperes (amps).

What is potential difference?

The work done moving a unit charge between 2 points in a circuit; V = W / Q.

What is resistance?

How difficult it is for current to flow through an appliance; R = V / I.

What defines an ohmic conductor?

A conductor that obeys Ohm's law, where current is directly proportional to potential difference under constant physical conditions.

How can you measure current in a circuit?

Using an ammeter connected in series with the component.

How do you measure potential difference across a component?

Using a voltmeter, connected in parallel across the component being measured.

What does the gradient of a current-potential difference graph represent?

The rate of change of current with respect to voltage, not equal to 1/R.

What indicates an ohmic conductor on a graph?

A constant gradient that passes through the origin, showing voltage is directly proportional to current.

Which graph indicates a higher resistance appliance?

Graph B, where a higher voltage is required for the same change in current compared to graph A.

What common appliance does the curve of a filament lamp represent?

As the current increases, the resistance also increases.

Why does increasing current in a filament lamp cause an increase in resistance?

As current flows, electrical energy converts to heat, causing metal ions to vibrate more, which impedes electron movement.

What is a diode?

An appliance that allows current to flow in only one direction.

When should you assume a voltmeter has infinite resistance?

Unless stated otherwise, to ensure no current flows through the voltmeter when connected in parallel.

Why should an ammeter be assumed to have zero resistance?

To ensure there is 0 potential difference across it, preventing energy loss and not affecting the circuit.

What is a Light Dependent Resistor (LDR)?

A semiconductor sensitive to light; its resistance decreases as light intensity increases.

How does a thermistor work?

It decreases resistance as temperature increases (negative temperature coefficient).

What is resistivity?

The resistance of a 1m cylinder with a cross-sectional area of 1m²; it is an inherent material property.

How can you determine the resistivity of a metal?

By measuring wire diameter, varying length, recording voltage/current, calculating resistance, and plotting a graph.

What is a superconductor?

A material with zero resistivity at or below a critical temperature.

How do you calculate total resistance in a series circuit?

RTotal = R1 + R2 + R3 + … (Add the individual resistances).

What is the voltage across 6 parallel cells each of 5V?

5V.

What is the voltage across 6 series cells each of 5V?

30V (5V x 6).

How does current vary in a series circuit?

The current through all components is the same and does not vary.

Is current the same in parallel components?

No, each branch can have different currents according to Kirchhoff’s first law.

What is Kirchhoff’s first law?

The current entering a junction equals the current leaving the junction.

What is Kirchhoff's second law?

The sum of all potential differences in a loop equals the total emf of the circuit.

What happens to emf when two cells are connected negative to negative in series?

They cancel out; total emf = ε1 - ε2.

What is power in terms of energy?

The rate of energy transfer.

How do you express power in terms of current and voltage?

Power = Current x Voltage, P = IV.

What is the purpose of a potential divider?

To provide variable or constant specific potential difference.

How do you find the voltage across a 7Ω resistor in a series with 6Ω and 7Ω resistors?

Voltage across 7Ω = (7/13) x 12 = 6.5V.

What is emf?

Electromotive force; electrical energy transferred by a power supply per unit charge.

What are two applications of superconductors?

1. Power cables reducing energy loss during transmission. 2. Strong magnetic fields for maglev trains and medical applications.

What is the total resistance of a parallel arrangement of 3Ω, 7Ω, and 9Ω resistors?

1 / RT = ⅓ + 1/7 + 1/9; RT = 1.7Ω.