9.3Physics 03. Electricity And Magnetism
Calculate resistance (resistance = voltage / current) and describe… — Cambridge Checkpoint Science 0893 Revision Notes & Topical Questions
5 min read 8 parts Lesson 3 of 5 1 quiz
9.3 Resistance, voltage and current — CHECKPOINT - Lower Secondary Science 0893 notes: Calculate resistance using resistance = voltage ÷ current and describe how resistance affects current.Resistance — a measure of how difficult it is for electrons to move through a material.It i…
- Effect on current
- Resistance equation
- Current equation
- Formula triangle
- Circuit symbol
- Filament — a thin wire with a high resistance that gets hot and glows when current flows
Section 1 of 8Resistance
- Resistance
- a measure of how difficult it is for electrons to move through a material.
- It is measured in ohms, with the symbol Ω.
- Effect on current
- the greater the resistance in a circuit, the smaller the current.
Section 2 of 8Resistance of materials
| Material | Resistance | Reason |
|---|---|---|
| Copper wire | Very low | Electrons move easily |
| Plastic insulator | Very high | Electrons cannot move |
| Lamp filament | High | Thermal energy makes it glow |
- Filament
- a thin wire with a high resistance that gets hot and glows when current flows.
Section 3 of 8Ohm's law
- Law
- voltage = current × resistance, written V = I × R.
- V is voltage in volts, I is current in amps and R is resistance in ohms.
- Resistance equation
- R = V ÷ I
- Current equation
- I = V ÷ R
- Formula triangle
- cover the quantity to find and use the other two.
Section 4 of 8Resistors
- Resistor
- a component designed to have a known resistance.
- Coloured bands on a resistor show its value in ohms.
- Circuit symbol
- a rectangle, with the value written beside it.
Section 5 of 8Finding the resistance of a component
- Connect the component in a circuit with a cell, an ammeter in series and a voltmeter in parallel.
- Measure the current through the component.
- Measure the voltage across the component.
- Divide the voltage by the current to get the resistance.
Section 6 of 8Current and voltage for a resistor
- Set up a circuit with one cell, a resistor, an ammeter and a voltmeter.
- Record the voltage and current.
- Add cells one at a time and record again.
- Plot voltage on the horizontal axis and current on the vertical axis.
- Result
- the graph is a straight line through the origin, so the current is proportional to the voltage.
Section 7 of 8Key terms
| Term | Meaning |
|---|---|
| Resistance | How difficult it is for current to flow through a material. |
| Ohm | The unit of resistance, Ω. |
| Ohm's law | Voltage = current × resistance. |
| Resistor | A component with a known resistance. |
| Filament | A thin wire in a lamp that glows when current flows. |
Section 8 of 8Exam technique
- Resistance and current are the same — the greater the resistance, the smaller the current.
- Copper has a high resistance — copper has a very low resistance.
- Resistance is measured in volts — it is measured in ohms.
- Insulators have no resistance — they have a very high resistance.
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