Download Document

23/05/2017
Producing and Measuring
Electricity
Edexcel
W Richards
The Weald School
DC and AC
23/05/2017
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
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 nonrechargeable
Zinc, carbon,
manganese,
lithium
Torches, clocks,
hearing aids
23/05/2017
Why use rechargeable batteries?
Why use standard batteries?
• Long long-term expense
• No need for charger
• Can be used many times
• Less expensive
• Less energy to produce
• Rechargeables contain carcinogens
Battery Capacity
23/05/2017
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?
Electric Current
Electric current is a flow
of negatively charged
particles (i.e. electrons).
+
e-
-
e-
23/05/2017
Note that
electrons go
from negative
to positive
Basic ideas…
23/05/2017
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
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
23/05/2017
23/05/2017
Electromagnetic
induction
The direction of the induced current is
reversed if…
1) The magnet is moved in the opposite
direction
2) The other pole is inserted first
The size of the induced current can be
increased by:
1) Increasing the speed of movement
2) Increasing the magnet strength
3) Increasing the number of turns on
the coil
Generators (dynamos)
23/05/2017
Induced current can be
increased in 4 ways:
1) Increasing the speed of
movement
2) Increasing the magnetic
field strength
3) Increasing the number of
turns on the coil
4) Increasing the area of the
coil
Resistance
23/05/2017
Resistance is anything that will
RESIST a current. It is measured
in Ohms, a unit named after me.
Georg Simon Ohm
1789-1854
The resistance of a component can be
calculated using Ohm’s Law:
Resistance
(in )
=
V
Voltage (in V)
Current (in A)
I
R
An example question:
23/05/2017
Ammeter
reads 2A
A
V
Voltmeter
reads 10V
1) What is the resistance across
this bulb?
2) Assuming all the bulbs are the
same what is the total resistance
in this circuit?
More examples…
23/05/2017
3A
6V
12V
3A
2A
4V
2V
1A
What is the
resistance of
these bulbs?
Resistance
23/05/2017
Resistance is anything that opposes an electric current.
Resistance (Ohms, ) =
Potential Difference (volts, V)
Current (amps, A)
What is the resistance of the following:
1) A bulb with a voltage of 3V and a current of 1A.
2) A resistor with a voltage of 12V and a current of 3A
3) A diode with a voltage of 240V and a current of 40A
4) A thermistor with a current of 0.5A and a voltage of
10V
Current-voltage graphs
I
23/05/2017
I
Low R
I
High R
V
3. Thermistor
1. Resistor
Current
increases in
proportion
to voltage
2. Bulb
V
As voltage increases
the bulb gets hotter
and resistance
increases
V
Resistance goes
down as the
thermistor gets
hotter (i.e.
more voltage)
LDRs and Thermistors
23/05/2017
LDRs and Thermistors
1) Light dependant
resistor – resistance
DECREASES when light
intensity INCREASES
Resistance
23/05/2017
2) Thermistor –
resistance DECREASES
when temperature
INCREASES
Resistance
Amount of light
Temperature
Electrical Inventions
Match these inventions with when they were invented:
Electric kettle
1876
Telephone
1882
Television
1891
Electric fire
1892
Electric iron
1908
Vacuum cleaner
1920s
23/05/2017
Computers
23/05/2017
Apple 1 (1976) – 1Mhz
IBM 5100 portable PC (1975), 25kg,
processor, 4K RAM, cost $670
1.9MHz processor, 64K RAM, 200K
internal tape storage, cost up to $20,000
Commodore 64 (1982) – 1Mhz
processor, 64K RAM, 16
colours, cost $600, 17m sold
Apple Macintosh (1984) – 8Mhz
processor, 512K RAM, cost $2500
Superconductivity
23/05/2017
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.
Heike Kamerlingh
Onnes (1853-1926)
The Maglev train is based on
superconductivity and uses
magnets to propel the train to
speeds of over 300mph.