1. Dynamic Electricity

2. What is a conductor and insulator? A conductor is a material which allows an electric current to pass. Metals are good conductors of electricity. An insulator is a material which does not allow an electric current to pass. Nonmetals are good conductors of electricity. Plastic, glass, wood, and rubber are good insulators

3. What is the difference between static electricity and current electricity ? Static electricity is stationary or collects on the surface of an object, whereas current electricity is the flow of electrons very rapidly through a conductor.

5. Current Intensity This is how many electrons are flowing through an electrical circuit every second. Current Intensity (I) is measured in amperes (A) 1 Amp is equal to 1 C per second. 1 C = 1 A 1 s I = q_I is current intensity (A), ∆t q is charge (C), ∆t = seconds (C stands for Coulomb, the unit of electrical charge)

6. Question A car headlight requires a current of 15 A. How much charge, in Coulombs are needed to operate the headlight for one minute?

7. Answer I = q/ ∆t, therefore q = I x ∆t q = 15 x 60 = 900 Coulombs of charge

8. The flow of electricity in current electricity has electrical pressure or voltage. Electric charges flow from an area of high voltage to an area of low voltage. Water pressure and voltage behave in similar ways.

9. Voltage is like the water pressure in the upper reservoir pushing the water through the pipe. The difference in pressure is called Potential Difference.

10. The unit used to measure voltage is volts (V). Voltage is calculated as the energy (joules) pushing each coulomb (C) of charge through the circuit. V = E V = voltage (V), E = energy (J) qq = charge (C) Question: How much energy is transferred by 200 C of charge in a home with 110 V voltage?

11. Answer V = E/q therefore E = V x q E = 110 x 200 = 22 000 joules of energy (Also, 22 kJ would be correct)

12. What are batteries ? Batteries are composed of a chemical substance which can generate voltage which can be used in a circuit. There are two kinds of batteries: dry cell and wet cell batteries. Below is an example of a dry cell. The zinc container of the dry cell contains a moist chemical paste surrounding a carbon rod suspended in the middle.

13. Wet cell batteries are most commonly associated with automobile batteries. A wet cell contains two connected plates made of different metals or metal compounds in a conducting solution. Most car batteries have a series of six cells, each containing lead and lead oxide in a sulfuric acid solution.

14. What is electrical resistance ? Resistance (R) is the opposition to the flow of an electric current, causing the electrical energy to be converted to thermal energy or light. The metal which makes up a light bulb filament or stovetop eye has a high electrical resistance. This causes light and heat to be given off.

15. ohm (Ω). The unit for measuring resistance is the ohm (Ω). Also, colder wires have less resistance than hot wires.

16. Electrical Calculations – What is Ohm’s Law? I = 3 V 2 Ω I = 1.5 amps

17. Power Electrical power is the amount of energy used by an electrical device every second. This energy can be used to perform work. P = E power is measured in watts (W) ∆ t energy is measured in joules (J)

18. Question An ipod device uses 12 watts of power. If it is run for 10 hours, how much energy is used?

19. Answer Power = energy/time therefore energy = power x time = 12 watts x 10 hours x 60 min x 60 sec = 432 000 joules

20. Another way to calculate power Power can also be calculated using Voltage and Intensity. P = VI Ex. if a television uses 110 watts at home and voltage is 110 V, How much current does it need?

21. Answer P = VI therefore I = P V I = 110 W = 1 amp 110 V

22. And… For really big quantities of energy we use kilowatts of power and hours of time. 1 kWh = 1000 watts x 3600 seconds = 3600 000 joules. We pay for electricity by the kWh, so it’s handy to know this calculation.

23. Example problem: E = P X time P = I V

24. Answer P = (2A) (120 V) = 240 W =.240 kW E = (.240 kW) (4 h) = 960Wh = 0.96 kWh (We pay about 7 cents per kWh of electricity in Quebec)

25. How is Electrical Power calculated? Electrical Power is the product of the current (I) and the voltage (v) The unit for electrical power is the same as that for mechanical power in the previous module – the watt (W) Example Problem: How much power is used in a circuit which is 110 volts and has a current of 1.36 amps? P = I V Power = (1.36 amps) (110 V) = 150 W