Electricity

    Cards (130)

    • Current is the flow of electrical charge
    • The unit of current is ampere (A)
    • Electrical charge will only flow around a complete (closed) circuit if there is a potential difference; a current can only flow if there's a source of potential difference.
    • In a single closed loop, the current has the same value everywhere in the circuit
    • Potential difference is the driving force that pushes the charge around.
    • The unit of potential difference is volt (V).
    • Resistance is anything that slows the flow of current down.
    • The resistance unit is ohm (Ω)
    • The current flowing through a component is dependent on the potential difference across it and the resistance of the component.
    • The greater the resistance across a component, the smaller the current that flows (for a given potential difference across the component)
    • Total charge through a circuit depends on current and time
    • The size of the current is the rate of flow of charge
    • When current flows past a point in a circuit for a length of time then the charge that has passed is given by a formula
    • Q=Q=ItIt
      Charge flow (coulombs, C) = Current (A) x Time (s)
    • More charge passes around a circuit when a larger current flows.
    • V=V =IR IR
      Potential difference (V) = Current (A) x Resistance (Ω)
    • The resistance of a circuit can depend on several factors, eg if the components are in series or parallel or the length of wires
    • The ammeter
      • measures the current in amps flowing through the test wire
      • must always be placed in series
    • The voltmeter
      • measures the potential difference of the test wire
      • must always be placed parallel, and not placed around any other component of the circuit
    • The length of a wire affecting resistance - RP3
      Aim:
      To investigate how the resistance of a wire depends on its length and how resistance varies in a series and parallel circuit
    • The length of a wire affecting resistance - RP3
      Equipment:
      • power supply
      • ammeter
      • voltmeter
      • resistance wire on meter ruler
      • leads and crocodile clips
      • switch
      • wire with no insulation
    • M1: wire length and resistance, RP3
      1. Set up the circuit as in the diagram
      2. Attach a length of wire along a meter ruler using pieces of tape
      3. Attach a crocodile clip to one end (x = 0cm on the ruler)
      4. Attach the second crocodile clip at x = 10cm on the ruler and record both current and pd through the wire
      5. Repeat by moving the crocodile clip 10cm along the wire and each time recording the current and the PD measured
      6. Calculate the resistance of the wire at each point using the equation V = IR
      7. Plot a graph of the length of the wire against the resistance of that wire at that point
    • M2: resistance
      Resistance in circuit
      1. construct a circuit with resistors arranged in series
      2. switch on the power supply and close the switch. Record current and PD shown
      3. construct a circuit with resistors arranged in parallel
      4. switch on the power supply and close the switch. record the PD and ammeter
      5. calculate the total resistance for each circuit using R = V/I
    • RP3 - Resistance
      safety precautions:
      • The uninsulated wire may become hot as current passes through it. Avoid handling the wire.
    • RP3 - wire length and resistance
      Outcome:
      The graph should be a straight line through the origin, meaning resistance is directly proportional to the length. The longer the wire, the greater the resistance.
    • What symbol is this?
      Variable resistor
    • Increasing the current in a filament lamp makes the temperature of the lamp increase and the resistance of the lamp increase.
    • When a potential difference is applied across a resistor, the energy transferred from the battery into the resistor causes the atoms in the resistor to vibrate more rapidly. As they do so, some of their kinetic energy is converted into thermal energy which increases the temperature of the resistor.
    • how to fix an LED that is not emitting light in a circuit?
      • reverse the connections to the LED
      • because an LED only allows current through one direction
    • E=E =QV QV
      energy transferred (J) = charge flow (C) x Potential Difference (V)
    • battery cell symbol?
    • switch (open) symbol?
    • switch (closed) symbol?
    • lamp symbol?
    • What is an electric current?
      - the flow of electric charge around a circuit
    • What is the unit of electric current?
      - ampere (A)
      - shortened to amp
    • How can we measure the current in a circuit?

      What is the symbol for this component?
      - by using an ammeter
    • How will the current be affected if we put this component in another position?
      - current is never used up in a circuit
      - in series, the current is the same all the way around
    • What direction does the electric current flow?
      - negative end of the cell to the positive end
    • How do lamps light up in a circuit?
      - electrons carry energy from the cell to the lamp
      => electrons pass this energy to the components in the circuit, e.g. the lamp
      => electrical energy transferred to light and thermal energy
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