1. Producing and Measuring Electricity
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Producing and Measuring Electricity
Edexcel
W Richards
The Weald School

2. DC and AC
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DC stands for “Direct Current” – the current only flows in one direction:
Time
1/50th s
AC stands for “Alternating Current” – the current changes direction 50 times every second (frequency = 50Hz)
240V T V

3. Types of Batteries Type of Battery Contains Uses Wet cell rechargeable
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Type of Battery
Contains
Uses
Wet cell rechargeable
Lead and acid
Cars, industry
Dry cell rechargeable
Nickel, cadmium, lithium
Mobile phones, power tools
Dry cell non-rechargeable
Zinc, carbon, manganese, lithium
Torches, clocks, hearing aids
Why use rechargeable batteries?
Long long-term expense
Can be used many times
Less energy to produce
Why use standard batteries?
No need for charger
Less expensive
Rechargeables contain carcinogens

4. Capacity (Ah) = Current (A) x Time (hours)
Battery Capacity
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The capacity of a battery is measured in Amp Hours (Ah). Basically, a battery with a capacity of 1Ah will provide a current of 1A for 1 hour.
Capacity (Ah) = Current (A) x Time (hours)
A battery provides a current of 2A for 2 hours. What was its capacity?
Another battery has a capacity of 10Ah. If it runs out after half an hour what current was being drawn?
A mobile phone battery has a capacity of 1100mAh. If it runs on a current of 250mA when being used in a phone call how long could the call last?

5. Electric Current
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Electric current is a flow of negatively charged particles (i.e. electrons).
Note that electrons go from negative to positive - + e- e-

6. Words: volts, amps, ohms, voltage, ammeter, voltmeter
Basic ideas…
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Electric current is when electrons start to flow around a circuit. We use an _________ to measure it and it is measured in ____.
Potential difference (also called _______) is how big the push on the electrons is. We use a ________ to measure it and it is measured in ______, a unit named after Volta.
Resistance is anything that resists an electric current. It is measured in _____. It usually increases when a device gets hot.
Words: volts, amps, ohms, voltage, ammeter, voltmeter

7. More basic ideas…
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If a battery is added the current will ________ because there is a greater _____ on the electrons
If a bulb is added the current will _______ because there is greater ________ in the circuit

8. Electromagnetic induction
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Electromagnetic induction
The direction of the induced current is reversed if…
The magnet is moved in the opposite direction
The other pole is inserted first
The size of the induced current can be increased by:
Increasing the speed of movement
Increasing the magnet strength
Increasing the number of turns on the coil

9. Generators (dynamos) Induced current can be increased in 4 ways:
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Induced current can be increased in 4 ways:
Increasing the speed of movement
Increasing the magnetic field strength
Increasing the number of turns on the coil
Increasing the area of the coil

10. Resistance V R I Resistance = Voltage (in V) (in ) Current (in A)
Georg Simon Ohm
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Resistance is anything that will RESIST a current. It is measured in Ohms, a unit named after me.
The resistance of a component can be calculated using Ohm’s Law: V R I
Resistance = Voltage (in V)
(in ) Current (in A)

11. An example question: Ammeter reads 2A A V
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Ammeter reads 2A V A
What is the resistance across this bulb?
Assuming all the bulbs are the same what is the total resistance in this circuit?
Voltmeter reads 10V

12. What is the resistance of these bulbs?
More examples…
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12V 4V 2A 1A 2V 3A
What is the resistance of these bulbs?

13. Resistance Resistance is anything that opposes an electric current.
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Resistance is anything that opposes an electric current.
Resistance (Ohms, ) = Potential Difference (volts, V)
Current (amps, A)
What is the resistance of the following:
A bulb with a voltage of 3V and a current of 1A.
A resistor with a voltage of 12V and a current of 3A
A diode with a voltage of 240V and a current of 40A
A thermistor with a current of 0.5A and a voltage of 10V

14. Current-voltage graphs
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Low R I
High R V
3. Thermistor
1. Resistor
Resistance goes down as the thermistor gets hotter (i.e. more voltage)
Current increases in proportion to voltage V
2. Bulb
As voltage increases the bulb gets hotter and resistance increases

15. LDRs and Thermistors
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16. LDRs and Thermistors
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1) Light dependant resistor – resistance DECREASES when light intensity INCREASES
2) Thermistor – resistance DECREASES when temperature INCREASES
Resistance
Amount of light
Resistance
Temperature

17. Electrical Inventions
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Match these inventions with when they were invented:
Electric kettle
Telephone
Television
Electric fire
Electric iron
Vacuum cleaner
1876
1882
1891
1892
1908
1920s

18. Computers Apple 1 (1976) – 1Mhz processor, 4K RAM, cost $670
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IBM 5100 portable PC (1975), 25kg, 1.9MHz processor, 64K RAM, 200K internal tape storage, cost up to $20,000
Apple 1 (1976) – 1Mhz processor, 4K RAM, cost $670
Apple Macintosh (1984) – 8Mhz processor, 512K RAM, cost $2500
Commodore 64 (1982) – 1Mhz processor, 64K RAM, 16 colours, cost $600, 17m sold

19. Heike Kamerlingh Onnes (1853-1926)
Superconductivity
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Heike Kamerlingh Onnes ( )
In 1911 I discovered superconductivity. This is when a metal can conduct electricity with zero resistance. I won the Nobel Prize for this discovery in 1913.
The Maglev train is based on superconductivity and uses magnets to propel the train to speeds of over 300mph.