Circuit diagrams and circuit components Flashcards – Cambridge IGCSE (9–1) Physics 0972 (Extended) (2026–2028)

How do electrical sources provide energy to a circuit?

By maintaining a potential difference between their terminals.

What energy conversion occurs in a cell?

Stored chemical energy is converted into electrical energy.

What is a battery?

Two or more cells.

What energy conversion occurs in a generator?

Mechanical energy is converted into electrical energy.

How is a cell represented in a circuit diagram?

Two parallel lines of unequal length; the longer line indicates the positive terminal.

How is a battery represented in a circuit diagram?

By repeating the cell symbol.

How may power supplies and generators be represented in circuit diagrams?

By source symbols or labelled terminals. A generator may be shown as a circle containing G.

How can the polarity and output type of electrical sources vary?

They depend on the source; the output may be direct or alternating.

What does a resistor do in a circuit?

It opposes current.

For a given potential difference, how does greater resistance affect the current through a resistor?

It gives a smaller current.

What is the difference between a fixed and a variable resistor?

A fixed resistor is intended to have constant resistance; a variable resistor can be adjusted to change its resistance and the circuit current.

How are fixed and variable resistors represented in circuit diagrams?

A fixed resistor is a rectangle; a variable resistor uses the resistor symbol with a diagonal arrow.

What does moving the control of a two-terminal variable resistor change?

The resistance in the conducting path.

What does a potential divider produce?

An output potential difference that is a fraction of the input potential difference.

How are two resistances arranged in a potential divider, and where is the output taken?

They are connected in series, and the output is taken across one part of the arrangement.

For a potential divider, what is the output potential difference across resistance $R$ in terms of the input potential difference and total series resistance? State the condition for this relationship.

$\dfrac{V_{\text{out}}}{V_{\text{in}}}=\dfrac{R}{R_{\text{total}}}$, provided no significant current is drawn from the output.

What are the two main components of a variable potential divider?

A resistive track and a movable contact, or slider.

Why does moving the slider of a variable potential divider change its output potential difference?

It changes the resistance on each side of the contact.

How is a variable potential divider represented in a circuit diagram?

A variable contact points to a resistive element; the slider provides an additional connection.

What is an NTC thermistor?

A temperature-sensitive resistor whose resistance decreases as its temperature increases.

At a fixed potential difference, how does increasing the temperature of an NTC thermistor affect the current through it?

The current increases as the thermistor’s resistance decreases.

How is a thermistor represented in a circuit diagram?

A resistor symbol crossed by a diagonal line with a short bar.

How does a thermistor differ from a manually adjusted variable resistor?

A thermistor’s resistance depends on temperature; a variable resistor is manually adjusted.

How does an LDR’s resistance change as the light intensity falling on it increases?

Its resistance decreases.

At a fixed potential difference across an LDR, what happens to the current if its resistance decreases?

The current increases.

What is the circuit symbol for an LDR?

A resistor with arrows pointing towards it to represent incident light, commonly enclosed in a circle.

What does an ammeter measure?

The current through a component or circuit path.

How is an ammeter connected to the circuit path being measured?

In series with the path.

What does a voltmeter measure?

The potential difference between two points.

How is a voltmeter connected to the component or section being measured?

In parallel across it.

How are the circuit symbols for an ammeter and a voltmeter distinguished?

Both are circles: the ammeter contains A, and the voltmeter contains V.

What resistance does an ideal ammeter have, and what effect does this have on the measured current?

Negligible resistance, so it does not significantly change the current.

What resistance does an ideal voltmeter have, and what effect does this have on the current it draws?

Very high resistance, so it draws negligible current.

What is the difference between an open and a closed switch?

A closed switch connects its contacts and allows current in the path. An open switch separates its contacts and breaks the path.

How does a circuit diagram represent an open or closed switch?

The symbol shows contacts with a movable connection: separated when open and joined when closed.

What effect does opening one branch have on current in parallel branches?

It prevents current in that branch but does not necessarily interrupt current in the other branches.

What is a relay?

An electrically operated switch.

How does an energised relay coil change the state of the switch contacts?

Current in the coil produces a magnetic field that moves an armature, changing the contacts’ state.

What does a relay allow one circuit to control?

A separate circuit, which may carry a larger current.

What happens to a relay’s contacts when its coil is no longer energised?

They return to their normal state.

In a relay diagram, what does a dashed link between the coil and contacts represent?

A mechanical link showing that the coil operates the contacts.

Must a relay’s control circuit and switched circuit be electrically connected to each other?

No, they need not be electrically connected.

How does a transformer transfer energy from its primary coil to its secondary coil?

An alternating potential difference across the primary creates a changing magnetic field, usually in a magnetic core. This field induces an alternating potential difference across the secondary.

Are the primary and secondary coils of a transformer normally directly electrically connected?

No.

How do step-up and step-down transformers change alternating potential difference?

A step-up transformer gives a larger secondary potential difference; a step-down transformer gives a smaller one.

What does a transformer’s circuit symbol look like?

Two coils facing one another, often with parallel lines between them representing the core.