Electricity Flashcards
Thermistor
The resistance of the thermistor depends on its temperature. At low temps the thermistor has a high resistance.
LDR (light dependent resistor)
At low light levels, LDR has high res
Where can u use LDR’s
Sensor in cameras or automatic lights that come on when it gets dark
Semi conductor diode
Allows current to flow in one direction only Current only flow in the other direction. Diodes are used to convert an alternating current into a direct current
Charge formula + units
QIT =
q= I * T
Charge = current * time
Charge = coulombs
Current = amps
Time = seconds
What two other factors other than amount of amps decide on the current through a component
The resistance of the component and the potential difference across the component
How do u measure potential difference across a component
A voltmeter must be placed in parrallel with that component.
Potential difference =
to calculate work power
Potential difference = energy/charge
Energy = joules
V=E/Q
Potential difference =
potential difference = current * resistance
A thinner wire increases what
resistance
A longer wire increase
resistance
Practical Changing the length of the wire affects its resistance
FIRST HALF steps 1-4
- Connect the circuit as shown in the diagram above.
- Connect the crocodile clips to the resistance wire, 100 cm apart.
- Record the reading on the ammeter and on the voltmeter.
4.Move one of the crocodile clips closer until they are 90 cm part
Practical Changing the length of the wire affects its resistance
SECOND HALF steps 5-8
- Record the new readings on the ammeter and the voltmeter.
- Repeat the previous steps reducing the length of the wire by 10cm each time down to a minimum length of 10 cm
7.Use the results to calculate the resistance of each length of the wire by using r=v/i, where R is the resistance V is the voltage and I is the current
8.Plot a graph of the resistance against the length for the resistance wire.
Practical Changing the length of the wire affects its resistance
HAZARDS
consequences
control measures
Heating of the resistance wire
burns the skin
Do NOT touch
Neutral wire color and purpose (2)
Blue that completes the circuit in a mains power supply
Ohmic conductor (2)
A conductor whose current flow is directly proportional to the potential difference across it. When held at a constant temperature.
Static charge
The charge caused by an imbalance of positive and negative charges in, or on an objects surface. It is often caused by electrons being rubbed from one surface to another.
Fixed resistor and potential difference relationship
They are directly proportional to eachother.
Relationship between filament bulb and potential difference sketch graph in paint.
https://bam.files.bbci.co.uk/bam/live/content/zcdnk2p/large
filament bulb relationship between energy input current to flow and the resistance potential difference and temprature
(5)
The more energy that is put into the bulb, the harder it is for the current to flow - the resistance of the bulb increases. As the potential difference increases, so does the temperature of the thin wire inside the bulb, the filament. The higher the temperature increases the vibrations of the ions which makes it harder for ions in the filament, which makes it harder for the electrons to get past.
Potential difference and current graph with semi conductor
Sketch in paint
https://bam.files.bbci.co.uk/bam/live/content/zwmb7p3/large
Circuit rules SERIES (2)
An electron will pass through every component on its way round the circuit. If one of the bulbs is broken then current will not be able to flow round the circuit. If one bulb goes out, they will all go out
How calculate total resistance in series circuit
Rtotal = R1+R2 ectr
Series circuits (3)
Current is the same through each component
Total potential difference of the power supply is shared between the components
The total resistance of the circuit is the sum of individual resistors
Circuit rules parallel
An electron will not pass through every component on its way round the circuit.
If one of the bulbs is broken then current will still be able to flow round the circuit through the other loop.
If one bulb goes out, the other will stay on
Current in parallel
Since there are different loops, the current will split as it leaves the cell and pass through one or other of the loops. An ammeter placed in different parts of the circuit will show how the current splits
Calculate current in parallel
i1= i2 + i4 = i3
How is potential difference shared around in parallel circuits
Equally
Resistors in parallel circuits
The supply current is divided between them. The overall resistance is reduced as the may