Lesson summary
10.1.1 Circuit Symbols — AS PHYSICS 9702 notes: Recognise circuit symbols and state the function of common components.Skill — being able to draw and interpret circuit diagrams using circuit symbols is essential.Recall — all the circuit symbols must be recognised and drawn.Switch …
- Fixed resistor
- Thermistor
- Light-dependent resistor (LDR)
- Light-emitting diode (LED)
- Closed switch
- Diode direction
Section 1 of 9Using circuit symbols
Skill
- Skill being able to draw and interpret circuit diagrams using circuit symbols is essential.
Recall
- Recall all the circuit symbols must be recognised and drawn.
Section 2 of 9Switch and fixed resistor
Switch
- Switch turns the circuit on when closed and off when open.
Fixed resistor
- Fixed resistor it limits the flow of current and has a resistance that cannot change.
Section 3 of 9Sensors
1Thermistor
- Thermistor its resistance depends on temperature, decreasing as temperature rises.
2Light-dependent resistor (LDR)
- Light-dependent resistor (LDR) its resistance depends on light intensity, decreasing as intensity rises.
Section 4 of 9Diodes
1Diode
- Diode allows current to flow in one direction only and is used to convert a.c. to d.c.
2Light-emitting diode (LED)
- Light-emitting diode (LED) equivalent to a diode that emits light when a current passes through it.
- Used for aviation lighting and displays such as TVs and road signs.
Section 5 of 9Meters
Ammeter
- Ammeter measures the current in a circuit and is connected in series.
Voltmeter
- Voltmeter measures the p.d. of a component and is connected in parallel.
Section 6 of 9Interpreting circuit diagrams
Closed switch
- Closed switch for current to flow the switch must be closed.
Diode direction
- Diode direction conventional current flows from positive to negative, so a forward-biased diode must point in this direction.
Section 7 of 9More from the specification
More from the specification
Electromotive Force of a Power Supply
- The electromotive force (e.m.f., ε) of an electrical power supply is the energy transferred from chemical or mechanical forms to electrical energy per unit electric charge passing through the source (ε = W / Q), measured in volts (V = J/C).
Potential Difference Across Components
- Potential difference (p.d., V) is the electrical energy transferred to other forms (heat, light) per unit charge passing between two points in a circuit (V = W / Q).
Electrical Power and Energy Transfer
- Electrical power P represents the rate at which electrical energy is transferred in a circuit, governed by the formulas P = I·V = I²·R = V² / R.
- (measured in watts, W)
Charge
- Quantity of electricity in coulombs, Q = It.What the symbols mean: Q = charge (C) · I = current (A) · t = time (s)
Terminal
- Connection point of a cell, labelled + or −.
Battery
- Two or more cells joined together.
Potential difference
- Work done by a unit charge passing through a component.
Energy transferred
- W = V Q, in joules.What the symbols mean: E or W = energy transferred (J) · Q = charge (C) · V = potential difference (V) · I = current (A) · t = time (s)
Electromotive force
- Energy transferred from other forms to electrical energy per unit charge.
Section 8 of 9Key terms
| Term | Meaning |
|---|---|
| Circuit symbol | Standard drawing that represents an electrical component. |
| Diode | Component that allows current in one direction only. |
| LED | Light-emitting diode that emits light when current passes through it. |
| Thermistor | Resistor whose resistance depends on temperature. |
| LDR | Resistor whose resistance depends on light intensity. |
Section 9 of 9Exam technique
1
Placing the ammeter in parallel — it must be in series.
2
Drawing the diode against the current direction so no current flows.
3
Leaving the switch open in a circuit that should conduct.
4
Confusing the LDR and thermistor symbols.