P2 REVISION – CHAPTER 7– Electricity Electrical Charges Electric Circuits Electric symbols If you rub two electrically insulating materials are rubbed together, __________________ are rubbed off one material and deposited on the other. Objects that have opposite electric charges ______________ each other, if they have the same electric charge they___________.   I is the current in amperes, A Q is the charge in coulombs, C t is the time in seconds, s. Every component has an agreed circuit symbol. Make sure you can recognise and draw them! Resistance Current is measured with an ammeter. Where are ammeters placed in relation to the component? What is the unit of current? The potential difference(pd) across a component is measured with a voltmeter. These are always placed in parallel with the component. What is the unit of potential difference?     V is ? W is ? Q is ? Don’t forget units! R is ? V is ? I is ? Don’t forget units! KEY WORDS: Insulating Electron Attract Repel Resistance Series ASSESSMENT: Ohm’s law: states that the current through a resistor at constant temperature is directly proportional to the potential difference across the resistor. 1

P2 REVISION – CHAPTER 7 – Electricity Cont. Current-Potential Difference Graphs Series Circuits A current-potential difference graph for a resistor. How are the components connected in a series circuit? What happens if there is a break in the circuit? Is the current the same or different through each component? If you add together the potential difference what does it give you? The resistance of the individual components add up to give the total resistance of the circuit. A current-potential difference graph for a filament bulb, line is a curve so the current is not directly proportional to the __________________ ___________________. Parallel Circuits The current in a diode flows in one direction only, in the reverse direction the diode has a very high resistance so the current will be what? How are the components connected in a series circuit? What happens if there is a break in the circuit? Is the pd across each component the same or different? The bigger the resistance of a component, the ______________ the current through it.   Use this equation to work out the current through a component in a parallel circuit. Thermistor: Resistance _______________ if its temperature increases. LDR: resistance decreases if the light intensity on it ___________. KEY WORDS: Diode Filament bulb Resistor Thermistor ASSESSMENT: 2

P2 REVISION – CHAPTER 7 – Mains Electricity Alternating Current Fuses Electrical Energy & Charge Direct current is supplied by cells and batteries and passes round the circuit in one direction. Alternating current is from the mains, how does it travel? Frequency of am ac supply can be worked out from an oscilliscope trace using the equation: How does a fuse work? Where is a fuse fitted in a circuit? How does a circuit breaker work? An electric current is the flow of what? What is the equation that relates to charge, current and time? When charge flows through a resistor, what makes it hot?   What can you use this equation for?   Cables & Plugs Electrical Power & Potential Difference Electrical Issues Electrical faults are dangerous what two things can they cause? Why must you check cables, plugs and sockets for damage regularly? What must you not touch with wet hands? Why are filament bulbs very inefficient?   Power can be calculated using the above equation.   Why are the pins of a plug made of brass? What does the earth wire earth? Why are some cables thicker than others? Using the current and the pd and the equation above enables us to calculate the power of an appliance. To work out the correct rating in amperes for a fuse rearrange the above equation, what would the equation now be? KEY WORDS: Current Frequency Oscilloscope Circuit breaker ASSESSMENT: 3