How much charge passes a point in a circuit when a current of 8A flows for 5s? 40 Coulombs

A charge of 120C passes through a battery in 4 minutes, what is a average current? 0.5 Amps

To start a car engine takes 80A for 6s, how much charge flows through the motor? 480 Coulombs

The beam current in an oscilloscope is 2mA, how many electrons strike the screen in 16s? 2 x 10 17 electrons

A charge of 20C flows through a 1 A charge of 20C flows through a 1.5V cell, how mush energy has been transferred from the cell. 30 Joules

Charge and Capacitors Charge = Current x time Total charge passed can be found from a I-t graph by…. Q= It only applies when current is constant. Charge is never used up in a circuit, it is conserved.

Student demo Separating material (dielectric) Aluminium sheets Watch out for dielectric breakdown – there is a limit to the amount of charge your capacitor can store

The circuit symbol for a capacitor It explains what it can be modelled as – two parallel plates

When a pd is applied, charge goes on. + 5 V 0V

+ 5 V 0V t = 0 s

+ - - + 5 V 0V + + - t = 1 s

+ - - + + 5 V 0V + - - + + - t = 2 s

+ - - + + 5 V 0V + - + - + - + - t = 3 s

Do the charges keep going on at the same rate? Why? + - - + + 5 V 0V + - + - + - + - t = 3 s What might happen when the charges come off?

+ - Electrons flow as shown during charge. One side of the capacitor becomes +, the other -

+ - As time goes on the charge builds…

+ - Until the capacitor is fully charged

+ - To discharge, we need to take the battery or cell away and complete the circuit To do this we may use a FLYING LEAD (deliberately loose lead) and a resistor to discharge the energy through

Electrons then flow back the way they came as it discharges. + - Electrons then flow back the way they came as it discharges.

This is a standard capacitor circuit This is a standard capacitor circuit. It has a flip switch that switches between the charging and discharging circuit.

Introduction to capacitors 470μF 100μF 220μF 6V Observe the ammeter deflection and voltmeter reading when the capacitor is charged and discharged.

E C A Writing up the experiment, work through in order. Outcome Grade Outcome Checklist E I can state the structure of a capacitor and describe what happens when a capacitor charges. Describe how charge is stored on the capacitor and what happens when you charge a capacitor. Draw a labelled diagram to help with your description Describe what you saw on both meters. C I can sketch the expected shape of p.d-t & I-t graphs for a capacitor discharging. I can explain she shape if the discharge graph Sketch what a graph of current against time would look like for charging and discharging. State the significance of the area under this graph? Try to relate this to the definition of an exponential. In what ways is this similar to our radioactivity work? A I can explain how and why resistance and capacitance affect the way a capacitor discharges What would these graphs look like if the capacitor were not discharged in between successive charges? Change the capacitor sizes. How does the graph change? Why? What does this tell you? What would happen if we were to add additional resistance to the circuit for charging and discharging? What do you think the p.d-time and charge-time graphs would look like for charging and discharging? Sketch them

Group Discussion on results Plenary 1 Group Discussion on results

Can you do the following ??? I can show my understanding of effects ideas and relationships… decay of charge on a capacitor modelled as an exponential relationship between charge and time, with the rate of removal of charge proportional to the quantity of charge remaining I can sketch, plot and interpret graphs of: decay of charge, current or potential difference with time for a capacitor (plotted both directly and logarithmically)