Current, Potential Difference and ResistanceAQA GCSE Physics: Flashcards
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Define electric current.
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- Define electric current.
- Electric current is the rate of flow of charge. It is measured in amperes (A) and represents the amount of charge flowing past a point in a circuit per unit time.
- Write down the equation that relates charge (Q), current (I), and time (t).
- Q = It, where Q is charge in coulombs (C), I is current in amperes (A), and t is time in seconds (s).
- Calculate the charge that flows when a current of 2 A passes through a circuit for 30 seconds.
- Q = It = 2 × 30 = 60 coulombs (C)
- Define potential difference.
- Potential difference is the energy transferred per unit charge. It is measured in volts (V) and represents the work done by the circuit per coulomb of charge that flows.
- Write down the equation that relates potential difference (V), energy transferred (W), and charge (Q).
- V = W/Q, where V is potential difference in volts (V), W is energy transferred in joules (J), and Q is charge in coulombs (C).
- Calculate the potential difference when 240 J of energy is transferred to move 40 C of charge.
- V = W/Q = 240 ÷ 40 = 6 volts (V)
- Define resistance.
- Resistance is a measure of how much a component opposes the flow of electric current through it. It is measured in ohms (Ω).
- State Ohm's Law and write the equation.
- Ohm's Law states that the potential difference across a conductor is directly proportional to the current flowing through it, provided temperature remains constant. The equation is V = IR, where V is potential difference (V), I is current (A), and R is resistance (Ω).
- Calculate the resistance of a component with a potential difference of 12 V and a current of 3 A.
- Using V = IR, rearranged to R = V/I: R = 12 ÷ 3 = 4 ohms (Ω)
- Explain how resistance varies with temperature in a metal (HT).
- As temperature increases in a metal, resistance increases. This is because the ions in the metal vibrate more vigorously at higher temperatures, causing more frequent collisions with free electrons, which impedes their flow and increases resistance.
- Explain in terms of ion vibration why the resistance of a metal increases when heated (HT).
- When a metal is heated, its ions vibrate with greater amplitude and frequency. The moving free electrons collide more often with these vibrating ions, experiencing more resistance to their motion. These increased collisions transfer energy and reduce the drift velocity of electrons, thereby increasing the overall resistance.
- Rearrange the equation V = IR to find current (I).
- I = V/R
- A wire has a resistance of 5 Ω and carries a current of 4 A. Calculate the potential difference across the wire.
- V = IR = 4 × 5 = 20 volts (V)
- Rearrange Q = It to find time (t).
- t = Q/I
- A current of 0.5 A flows for a certain time and transfers 25 C of charge. Calculate the time taken.
- Using t = Q/I: t = 25 ÷ 0.5 = 50 seconds (s)