Circuits and resistance Flashcards
What is current?
What is the unit?
The flow of electric charge round a circuit.
Amps, A
When only will current flow?
Through a component if there is potential difference across the component
What is potential difference?
What is the unit?
The driving force that pushes the current around
V, Volts
What is resistance?
What is the unit?
Resistance is …
anything in the circuit which slows the flow of electricity down
ohm, the o with feet stuck out out the outsides
futile
What is the rule about resistance across a component?
The greater the resistance across a component the small the current that flows (for a given p.d across the component)
Current is the … of flow of …
What is the equation for current?
rate of flow of charge
Current (A) = charge (C) / time (s)
What is a charge measured in?
More charge passes around the circuit when a bigger … flows.
Coulombs, C
current
P.D is the …. …. per Coulomb of ….. that passes bewteen …. …. on an electrical circuit
work done, charge, two points
What is the formula for P.D?
So the P.D across an electrical component is the amount of …. …. by that electrical component per … … ……
P.D = work done / charge
energy transferred, per unit of charge
Voltage and P.D ….
mean the same thing
What does the symbol for a cell look like?
Horizontal line joint to a vertical like a sideways T, with another T the opposite way round, head to head with a gap, but T2 is smaller and thicker, just the top of the T not the wire
What does the symbol for a battery look like?
Horizontal T, with another T the opposite way round, head to head with a gap, but T2 is smaller and thicker, just the top of the T not the wire, the wire is dashed to form the stand of the next T that meats another thick T that continues onto the circuit.
What does an open switch look like?
two circles with a stick like a gate between them that is open, not touching the second dot
What does a closed switch look like?
two circles with a stick like a gate between them that is resting on the second dot, in contact, and closed
What does a filament lamp diagram look like?
A circle with a black X through the middle
What does a fuse diagram look like?
a rectangle on the wire line which you can see running through it
What does an LED, light emitting diode diagram look like?
a circle with a triangular arrow point in the direction of current low with a vertical line at its tip, inside the circle, with two arrows outside of the circle pointing upwards to represent light.
What does a resistor diagram look like?
the wire with a blank rectangle on it. You CAN’T see the wire running through it.
What does a variable resistor diagram look like?
a resistor, a blank rectangle, with a straight arrow going from left to right across it.
What does an ammeter diagram look like?
A circle with a capital A in it
What does a voltmeter diagram look like?
A circle with a capital V in it
What does a diode diagram look like?
a circle with a triangular arrow point in the direction of current low with a vertical line at its tip, inside the circle
What does a light dependent resistor (LDR) diagram look like?
a circle on the line, the line goes inside the circle but stops at the square inside, the resistor, then comes out the other end. There are two arrows outside of the circle pointing in representing light.
What does a thermistor diagram look like?
a blank rectangle, with a line across it that runs parallel to the box (below it) for a little bit then goes up like the ticks do, across the themristor
Describe the circuit needed to find the resistance of a component….
1. What is the power supply and which was does the energy flow?
2. What is the first component?
3. Next?
4. What happens here, what’s the lower part, and then the upper…
The end. What graph would the results from this give?
Why can the components be put in any order?
- A cells, thick T on the left, thin on the right, where the elecy is flowing from, it is going clockwise around the circuit
- A variable resistor with a tick going upwards against the flow of elecy
- An ammeter
- A voltmeter is joined on blow the circuit in parallel with a component above it.
- A volt - current (I) graph to find the resistance
- they are in series
What does the ammeter do in the circuit needed to find the resistance of a component?
Where must it be placed?
Measures the current in amps, flowing through the component
In series, (in the circuits main line), but anywhere in the circuit, just not in parallel
What does the voltmeter do in the circuit needed to find the resistance of a component?
Where must it be placed?
Measures the P.D across the component
In parallel around the component being tested
As you alter the variable resistor what happens in the circuit?
the current flowing through the circuit changes
Describe what the graph looks like for a bunch of tested different resistors… 1. Axes
2. Where do the lines go?
The current through the resistor (at a … temp) is … ….. to the P.D.
Different …. have different ….. hence the different gradients
- I-current, on the y, V on the x
- All at different gradients the straight lines all run through 0 from the - - quarter to the ++ quarter
constant, directly proportional
resistors, resistances
Describe what the graph looks like for a filament lamp… 1. Axes
2. Where do the lines go?
As the temp of the ….. ….., the …. increases, hence the curve
- I-current, on the y, V on the x
- In an s shaped curve from the – box to ++ through 0, reasonably shallow
filament, increases, resistance,
Describe what the graph looks like for a diode… 1. Axes
2. Where do the lines go?
Current will only … through a diode in … ……. . The diode has a …. …… ………… in the opposite direction
- I-current, on the y, V on the x
- Along 0 on the x axis then after a couple of squares in the ++ box it does an exponential curve shape.
flow, one direction, very high resistance
Resistance ….. with temperature
What happens when electrical charge flows through a resistor?
This …. …. causes the … to … more.
This makes it … …… for the …..-…….. to get through the ….
The … can’t … as easily and the …… …….
increases
some of the elecy energy is transferred into heat energy and the resistor gets hot
heat energy, the ions to vibrate more
more difficult, charge-carrying, resistor
current, flow, resistance increases
For most resistors there is a … to the amount of … that can …
More current means an …. in …. which means an …. in …., so the …. ….. again
This is why the …… ….. levels off on it’s ….. at … currents
limit, current, flow
increase, temp, increase, resistance, current , decreases
filament lamp, graph, high
What is the equation for resistance?
Rearrange to get the equation for P.D?
Resistance = Voltage / current P.D = Current x voltage
On the graph for the different resistors the resistance of the component was …… and is equal to the ….. of the gradient of the line. 1/gradient.
So the steeper the …. the lower the …
If the graph ….. then the … is ….. .
steady, inverse
graph, resistance
curves, resistance, changing
Describe a diode….
- What is it (simple) and made of?
- What is it used for?
- What does it do?
- Where is this useful?
A special device made of a semiconductor material such as silicon
To regulate the P.D across the circuit
Lets current flow freely through it in one direction but not the other (there’s a high resistance in the other direction)
4. Useful in various electronic circuits
Describe a light - emitting diode….
- What does it do in the circuit?
- What is it used for and why?
- What does it do in relation to their uses?
- Where are they used?
- Emits light when a current flows through it in a forward direction
- Lighting and use a much smaller current than other forms of lighting
- Indicate the presence of current in a circuit, often used in appliances, TVs, to show that they’re switched on
- Used for the numbers on digital clocks, in traffic lights and in remote controls
Describe a light dependent resistor….
- What is it?
- In bright light the resistance…
- In darkness the resistance is ….
- Where are they used?
- What does the graph look like?
- A resistor that is dependent on the intensity of light
- The resistance falls
- highest
- Lots of application with automatic night lights, outdoor lighting and burglar detectors
- A downwards slope with x as light intensity an y as resistance in ohms, dark in the corner, light on the right.
Describe a thermistor….
- What is it?
- In hot conditions the resistance…
- In cold conditions the resistance is ….
- Where are they used?
- What does the graph look like?
- A temperature dependent resistor
- drops
- goes up
- useful temp detectors e.g car engine temp sensors or electronic thermostats
- The same as the LDR but with cool in the corner and hot on the outside
