Producing%20and%20Measuring%20Electricity

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Producing and Measuring Electricity
Edexcel
W Richards The Weald School
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DC and AC
V
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
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Types of Batteries
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

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Battery Capacity
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)

1. A battery provides a current of 2A for 2 hours.
   What was its capacity?
2. Another battery has a capacity of 10Ah. If it
   runs out after half an hour what current was
   being drawn?
3. 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?

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Electric Current
Electric current is a flow of negatively charged
particles (i.e. electrons).
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Basic ideas
Words volts, amps, ohms, voltage, ammeter,
voltmeter
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More basic ideas
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
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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

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Generators (dynamos)

• 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

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Resistance
The resistance of a component can be calculated
using Ohms Law
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An example question

1. What is the resistance across this bulb?
2. Assuming all the bulbs are the same what is the
   total resistance in this circuit?

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More examples
6V
12V
What is the resistance of these bulbs?
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Resistance
Resistance is anything that opposes an electric
current.

• 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

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Current-voltage graphs
3. Thermistor
1. Resistor
Resistance goes down as the thermistor gets
hotter (i.e. more voltage)
Current increases in proportion to voltage
2. Bulb
As voltage increases the bulb gets hotter and
resistance increases
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LDRs and Thermistors
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LDRs and Thermistors
2) Thermistor resistance DECREASES when
temperature INCREASES
1) Light dependant resistor resistance
DECREASES when light intensity INCREASES
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Electrical Inventions
Match these inventions with when they were
invented
Electric kettle Telephone Television Electric
fire Electric iron Vacuum cleaner
1876 1882 1891 1892 1908 1920s
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Computers
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Superconductivity
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.