IB MYP 4-5 Physics- Potential difference - Study Notes - New Syllabus
IB MYP 4-5 Physics-Potential difference – Study Notes
Key Concepts
- Potential difference
Potential Difference (Voltage)
Potential Difference (Voltage)
Potential difference (p.d.), also called voltage, is the work done to move a unit charge between two points in a circuit.
- It is the “push” that drives charges through a circuit.
- It measures the energy per unit charge supplied or used.
- A voltmeter is always connected in parallel across a component to measure the p.d. across it.
Formula for potential difference:
\( V = \dfrac{W}{Q} \)
where:
- \( V \) = potential difference (V, volts)
- \( W \) = work done or energy transferred (J, joules)
- \( Q \) = charge (C, coulombs)
Key Points
- 1 volt (1 V) means that 1 joule of work is done to move 1 coulomb of charge.
- Potential difference across the battery shows the energy provided to charges.
- Potential difference across a resistor, lamp, or device shows the energy transferred from the charges to that component.
- In a series circuit: total potential difference is shared among components.
- In a parallel circuit: potential difference across each branch is the same as the source.
Difference Between p.d. and E.M.F.
| Feature | Potential Difference (p.d.) | Electromotive Force (E.M.F.) |
|---|---|---|
| Definition | Energy transferred from charges to a component per unit charge | Energy supplied to charges by the source per unit charge |
| Occurs | Across a component (e.g. resistor, lamp) | In the source (e.g. battery, generator) |
| Meaning | Represents energy used by the charges | Represents energy provided to the charges |
| Measurement | With a voltmeter across a component | With a voltmeter across cell (open circuit) |
Example:
A 12 V battery provides 24 C of charge. How much energy is transferred?
▶️ Answer/Explanation
Using \( V = \dfrac{W}{Q} \) → \( W = VQ \).
\( W = 12 \times 24 = 288 \, J \).
Final Answer: \( \boxed{288 \, J} \).
Example:
A lamp transfers 60 J of energy when 20 C of charge flows through it. What is the p.d. across the lamp?
▶️ Answer/Explanation
\( V = \dfrac{W}{Q} = \dfrac{60}{20} = 3.0 \, V \).
Final Answer: \( \boxed{3.0 \, V} \).
Example:
A 9 V battery is connected in series with two resistors. The voltmeter across one resistor reads 4 V. What is the potential difference across the other resistor?
▶️ Answer/Explanation
In series, total voltage is shared. Total p.d. = 9 V. One resistor has 4 V.
Other resistor must have \( 9 – 4 = 5 \, V \).
Final Answer: \( \boxed{5 \, V} \).