P2:Electricity Flashcards
Give 2 rules when drawing a circuit diagram:
1) make sure all the wires in your circuit are straight lines.2) make sure the circuit is closed.
Total charge through a circuit depends on….
Current and time.
Electric current is a flow of….
electric charge.
Current is measured in….
Amperes ( A)
Charge is measured in…
Coulombs (C)
Electric charge will only flow around a complete circuit if something is providing a potential difference. Give an example of a PD:
A battery - it is a ‘driving force’ that pushed charge around the circuit.
What is resistance?
Anything that slows down the flow of charge.
What does the size of a current tell you?
How fast the charge is flowing - this is known as the rate of flow charge.
Give the equation for finding the rate of CHARGE FLOW:
Charge flow = CURRENT X TIME
The current flowing through a component depends on: (2)
- The potential difference across it.- The resistance of the component.
If there is a big resistance across a component, how does this affect the current that flows through?
The smaller the current.
Give the formulae for finding the potential difference:
CURRENT in amps X RESISTANCE in ohms
What are Ohmic Conductors?
Components with a fixed resistance. This means the resistance of the component doesn’t change with current.
Ohmic Conductors only have a fixed resistance if ………….. doesn’t change.
Their temperature.
Give 2 examples of Ohmic Conductors:
- Wires- Resistors
What is the link between the current and the potential difference in an Ohmic Conductor?
The current flowing through it is directly proportional to the potential difference across it. Meaning that of the potential difference doubles, so does the current.
Some components have a resistance that DOES change with the current. Explain how this works for a FILAMENT LAMP:
Filament lamps contain a wire which is designed to heat up and ‘glow’ as the current increases so as the current increases, the temperature of the filament increases too. Resistance increases with temperature so the resistance increases with current.
How does resistance work on DIODES?
The resistance depends on the direction of the current. It will let current flow in one direction but it has a very high resistance in the opposite direction which makes it hard for a current to flow that way.
The resistance of a circuit can depend on a number of things. Give 2 examples:
- If components are in series or parallel.- The length of wire used in the circuit.
Give the 7 steps to investigating the effect of wire length in a circuit:
1) Attach a crocodile clip to the wire level with 0cm on the ruler.2) Attach the second crocodile clip to the wire a short distance from the first clip.3) Write down the length of the wire between the clips.4) Close the switch, record the current through the wire and the potential difference across it..5) Calculate the resistance of the wire using the equation.6) Open the switch and move the second crocodile clip along the wire.7) Repeat steps for a range of wire lengths.
How to plot a graph of your results AFTER INVESTIGATING THE EFFECT OF WIRE LENGTH IN A CIRCUIT: (4)
1) Plot a graph of resistance against wire length.2) Draw a line of best fit through your points.3) Your graph should be a straight line through the origin.4) This means resistance is directly proportional to length - the longer the wire, the greater the resistance.
What is “I-V Characteristics”?
A graph showing how the current flowing through the component changes as the potential difference across it changes.
What are components with STRAIGHT LINE IV Characteristics called? Give an example.
Linear Components. (e.g. a fixed resistor)
What are components with CURVED IV Characteristics called? Give an example.
Non-linear components (e.g.filament lamp or diode)
Give the 6 steps to investigating IV Characteristics on different components:
1) Set up a test circuit (the one on page 183 in revision guide)2) The variable resistor is used to change the current in the circuit. This changes the potential difference across the component.3) Set the resistance of the variable resistor and measure the current through and potential difference across the component.4) Swap over the current connected to the cell to reverse the direction of the current. The ammeter should now display negative readings.5) Repeat step 3 to get results for negative values of current.6) Plot a graph with current on the y axis and the potential difference on the x axis.
LDR is short for…
Light Dependant Resistor.
LDR - In bright light, is the resistance high or low?
LOW.
LDR - In darkness, is the resistance high or low?
HIGH.