Starter

1. Starter In pairs try and explain…. What current is, What electric charge is, Why electrons are negatively charged, Why are electrons called electrons.

2. 1.1.4 Projectile Motion CHARGE!

3. G482 At GCSE you had to KNOW about electricity. At AS Level you have to UNDERSTAND electricity.

4. Unit G482: Electrons, Waves and Photons • Module 1: Electric current • 2.1.1 Electric current • Module 2: Resistance • 2.2.1 Circuit symbols • 2.2.2 E.m.f. and p.d. • 2.2.3 Resistance • 2.2.4 Resistivity • 2.2.5 Power • Module 3: DC circuits • 2.3.1 Series and parallel circuits • 2.3.2 Practical circuits

5. Learning outcomes You should all be able to: • explain that electric current is a net flow of charged particles; • explain that electric current in a metal is due to the movement of electrons, whereas in an electrolyte the current is due to the movement of ions; • explain what is meant by conventional current and electron flow;

6. Extended Learning task • Read the specification for G482 Electrons, Waves and Photons. • In AdvancedPhysicsfor You read pages 190 – 195. • Take appropriate notes that you feel will help you understand current and charge. • Complete questions 1 – 6 on page 204.

7. Explain how a charged rod can attract a neutral piece of paper. How large a piece of paper can you pick up?

8. Explain how a charged rod can attract a neutral piece of paper. How large a piece of paper can you pick up?

9. Learning outcomes You should be able to: • select and use the equation ΔQ = IΔt; • define the coulomb; • recall and use the elementary charge e = 1.6 × 10-19 C. • describe how an ammeter may be used to measure the current in a circuit; • describe Kirchhoff’s first law and appreciate that this is a consequence of conservation of charge;

10. Key Definition 1 coulomb is the amount of charge that passes a point when a current of 1 ampere flows for 1 second.

11. The challenge • Gustav Kirchhoff said that: “The sum of currents flowing into a point equals the sum of the currents flowing out of that point.” • You are to set up a number of circuits to prove Kirchhoff’s 1st law • Think about the resources you have available for your group and the data you need to collect.

12. internal 50MW resistor 5 kV supply link to earth socket bare 4mm plug insulating handle metal disk on 4mm plug 044 coulomb meter Spooning amounts of charge

13. A spoonful of electrons makes the medicine go down Knowing that the charge on an electron is –1.6 x 10–19 C, you can calculate the number of electrons in a 'spoonful' of charge. A typical spoonful of negative charge is –2 nC. So the number of electrons is…..

14. 1. Convert 25 mA to A 2. Convert 0.50 A to mA 3. A torch bulb passes a current of 120 mA. (a) How many coulombs of charge flow through the lamp in 1 minute? (b) How many coulombs of charge flow through the lamp in 1 hour? (c) How many electrons leave the negative terminal of the cell each second? 4. A car battery is rated as 36 A h. In principle this means it could pass a current of 1 A for 36 h before it runs down. How much charge passes through the battery if it is completely run down? 5. An electron beam in a beam tube carries a current of 125 A. (a) What charge is delivered to the screen of the tube every second? (b) How many electrons hit the screen each second?

15. Solutions to introductory questions on charge and current 1. 0.025 A 2. 500 mA 3. (a) Q = It = 0.120  60 = 7.2 C (b) Q = It = 0.120  60  60 = 432 C (c) N = Q/e = It/e = (0.120  1) / 1.6  10-19 = 7.5  1017 s-1 4. Q = It = 36  60  60 = 129 600 = 130 000 (2 sf.) 5. (a) Q = It = 1.25  10-4 1 = 1.25  10-4 C (b) N = Q/e = 1.25  10-4 / 1.6  10-19 = 7.8  1014 s-1

16. Learning outcomes