PHYSICS UNIT 2 Physics P2 for GCSE Additional Science or GCSE Physics

AQA GCSE Science PHYSICS 2 Unit P2.3 Currents in electrical circuits

• The current in an electric circuit depends on the resistance of the components and the supply.

• You should be able to use their skills, knowledge and understanding to:

  • apply the principles of basic electrical circuits to practical situations,

  • evaluate the use of different forms of lighting, in terms of cost and energy efficiency,

  • and examples might include filament bulbs, fluorescent bulbs and light-emitting diodes (LEDs).

AQA GCSE Science PHYSICS Unit P2.3.1 Static electricity

• a) Know and understand that when certain insulating materials are rubbed against each other they become electrically charged. Negatively charged electrons are rubbed off one material and onto the other.

• b) Know and understand that the material that gains electrons becomes negatively charged.

  • Know the material that loses electrons is left with an equal positive charge.

• c) Know and understand that when two electrically charged objects are brought together they exert a force on each other.

• d) Know that two objects that carry the same type of charge repel and two objects that carry different types of charge attract.

• e) Know that electrical charges can move easily through some substances, eg metals.

AQA GCSE Science PHYSICS Unit P2.3.2 Electrical circuits

• a) Know and understand that electric current is a flow of electric charge.

  • Know the size of the electric current is the rate of flow of electric charge.

  • Know that the size of the current is given by the equation:

    • Be able to use the equation:

    • I = Q / t   (Q = It)

    • I is the current in amperes (amps), A

    • Q is the charge in coulombs, C

    • t is the time in seconds, s

• b) Know and understand that the potential difference (voltage) between two points in an electric circuit is the work done (energy transferred) per coulomb of charge that passes between the points.

  • Be able to use the equation:

  • V = W / Q  (W = VQ)

  • V is the potential difference in volts, V

    • You can use either of the terms potential difference or voltage but questions will be set using the term potential difference.

  • W is the work done in joules, J

  • Q is the charge in coulombs, C

• c) You need to be able to draw or interpret circuit diagrams using standard symbols

  • You should know the standard symbols shown on the right.

  • Knowledge and understanding of the use of thermistors in circuits, eg thermostats is required.

  • Knowledge and understanding of the applications of light-dependent resistors (LDRs) is required, eg switching lights on when it gets dark.

• d) Appreciate that a current–potential difference graphs are used to show how the current through a component varies with the potential difference across it.

• e) Know and understand the current–potential difference graphs for a resistor at constant temperature - see graph.

• f) Know and understand that the resistance of a component can be found by measuring the current through, and potential difference across, the component.

• g) Know and understand that the current through a resistor (at a constant temperature) is directly proportional to the potential difference across the resistor.

• h) Be able to calculate current, potential difference or resistance using the equation:

  • Be able to use the equation:

  • V = I x R    ( V = IR, I = V/R, R = V/I)

  • V is the potential difference in volts, V

  • I is the current in amperes (amps), A

  • R is the resistance in ohms, Ω

• i) Know and understand that the current through a component depends on its resistance.

  • Know the greater the resistance the smaller the current for a given potential difference across the component.

• j) Know and understand that the potential difference provided by cells connected in series is the sum of the potential difference of each cell (depending on the direction in which they are connected).

• k) Know and understand that for components connected in series:

  • the total resistance is the sum of the resistance of each component

  • there is the same current through each component

  • the total potential difference of the supply is shared between the components.

• I) Know and understand that for components connected in parallel:

  • the potential difference across each component is the same

  • the total current through the whole circuit is the sum of the currents through the separate components.

• m) Know and understand that the resistance of a filament bulb increases as the temperature of the filament increases - see graph.

  • HT only: You should be able to explain resistance change in terms of ions and electrons.

• n) Know and understand that the current through a diode flows in one direction only - see graph.

  • Know that the diode has a very high resistance in the reverse direction.

• o) Know and understand that an LED emits light when a current flows through it in the forward direction.

  • You should know that there is an increasing use of LEDs for lighting, as they use a much smaller current than other forms of lighting.

• p) Know and understand that the resistance of a light-dependent resistor (LDR) decreases as light intensity increases.

• q) Know and understand that the resistance of a thermistor decreases as the temperature increases.

  • Knowledge of a negative temperature coefficient thermistor only is required.

• Practical work in unit 2.3 to help develop your skills and understanding may have included the following:

  • using filament bulbs and resistors to investigate potential difference/current characteristics,

  • investigating potential difference/current characteristics for LDRs and thermistors,

  • setting up series and parallel circuits to investigate current and potential difference,

  • planning and carrying out an investigation to find the relationship between the resistance of thermistors and their temperature,

  • investigating the change of resistance of LDRs with light intensity.