BRAINCAKEElectricity and magnetism
Revision notes for Electricity and magnetism in OCR Combined Science A (J250). Every lesson in BrainCake comes with R.E.C.I.P.E. recall steps, a quick check and spaced reviews.
- Charge and matterCharge is a property of all matter.
- Producing static electricityStatic electricity is made when two insulating materials are rubbed together.
- Electron transfer and staticAtoms contain positive protons in the nucleus and negative electrons around it.
- Current and the flow of chargeAn electric current is the rate of flow of charge.
- Current in a closed loopIn a single closed loop, the current has the same value at every point.
- Charge, current and timeThe amount of charge that flows past a point depends on the current and on how long it flows for.
- Series and parallel circuitsIn a series circuit the components are connected one after another in a single loop, so the current has only one path.
- Circuit symbols and d.c. conventionsCircuits are drawn as diagrams using standard symbols joined by straight lines.
- Current, potential difference and resistanceCurrent (I) is the rate of flow of charge.
- The relationship between I, R and VThe potential difference, current and resistance of a component are linked by one equation: potential difference = current × resistance, or V = I R.
- Why resistance can changeResistance happens because the moving electrons collide with the ions in the material.
- Circuits to investigate resistanceTo explore how a component behaves, build a test circuit.
- Using graphs to show linear and non-linear circuit elementsTo find out how a component behaves, you plot a graph of current against potential difference (an I-V graph).
- Relating I-V curves to the properties of circuit elementsThe shape of an I-V graph tells you how a component works.
- Why resistors in series and in parallel change the net resistanceIn a series circuit there is only one path.
- Calculating currents, potential differences and resistances in series and parallel circuitsThe key equation is potential difference = current × resistance (V = IR).
- Designing and using d.c. circuits for measurement and testingA d.c. circuit can be used to measure the resistance of a component and to test how it behaves.
- Power, potential difference, current and energy transferThe power of a device is the energy it transfers each second.
- Circuit calculations with resistors in seriesThese equations link the quantities in a d.c. circuit.
- Attraction and repulsion between magnetic polesEvery magnet has two ends called poles, a north pole and a south pole.
- Permanent and induced magnetsA permanent magnet, such as a bar magnet, produces its own magnetic field all the time.
- Magnetic fields around a magnetA magnetic field is the region around a magnet where another magnet or a piece of magnetic material feels a force.
- The Earth's magnetic field and a dipping compassA compass needle is a small magnet that is free to turn, so it lines up with any magnetic field it is in.
- Magnetic field around a current-carrying wireA wire carrying an electric current is surrounded by a magnetic field.
- Strength of the field around a wireThe magnetic field around a current-carrying wire is not the same strength everywhere.
- Solenoids and electromagnetsA solenoid is a long coil of wire.
- Force on a current-carrying wireA wire carrying a current has a magnetic field around it.
- Fleming's left-hand ruleFleming's left-hand rule gives the direction of the force on a wire that carries a current at right angles to a magnetic field.
- Force on a conductor: F = BILA wire at right angles to a uniform magnetic field experiences a force.
- Electric motorsAn electric motor uses the force on a current-carrying wire in a magnetic field to make a coil rotate.