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59 Cards in this Set
- Front
- Back
- 3rd side (hint)
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Draw a basic example of a circuit. This circuit must have a cell supplying 6V (6 volts) to the circuit, and a resistor and ammeter in series with each other. Label which part of the cell is + and - as well. |
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What is the voltage supplied to a circuit equal to and under what circumstance is this the case? |
Voltage supplied(V) = electromotive force (emf) or (epsilon)
As long as internal resistance is negligible. |
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What is the definition of voltage?
What is the equation to calculate voltage? |
Voltage: work done per unit charge.
V = E/Q |
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If 6V is flowing in a circuit, how much work is being done per coulumb of charge? |
6J (Joules) of work is being done per coulomb of charge. |
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What is the charge of an electron? |
-1.6 x 10^-19 C (Coulombs) |
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In circuits, cells and batteries have a positive end and a negative end. The picture shows a cell and a battery. Label which end is:
Positive Negative
On on both the cell and the battery. |
Longer end +ve Shorter end -ve. |
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In a circuit, what are the two types of flows? Draw in this circuit what direction the two flow types would be going in. Also state whether it's going from the positive end to the negative end, or the negative end to the positive end. |
Conventional current flows (the direction the current goes in) Electron flows (the direction the electrons go in) |
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What are voltmeters used for?
Where are voltmeters ALWAYS placed in a circuit and why? |
Measuring voltage across a component, thus measuring the energy lost by each coulumb of charge across that component.
Voltmeters are always placed PARALLEL to a component (Such as resistors, light bulbs etc). This is so they can measure the voltage/pd across the conponent. |
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Draw where a voltmeter could go in this circuit. |
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What do ammeters measure? Where do ammeters ALWAYS go in a circuit? |
Current Ammeters are always connected in SERIES to a component. |
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What is the definition of current?
What is the equation to calculate current? |
Rate of flow of charge
I is current (Amps, A)
Q is charge (Coulombs, C)
t is time. (Seconds, s) |
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If voltage were to increase whilst everything else remains constant, what does that do to electrons?
What does this change in the electrons do to current and why? |
Makes them go faster
This increases current, since the electrons are flowing faster. Current is rate of flow of charge. |
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Draw a current against voltage graph for a standard resistor. Explain why the graph looks like this. |
The graph is a straight line because electrons flow quicker (current increases) when more voltage is applied. |
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What is the Ohm's Law equation? |
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What is the unit for resistance? |
Ohms |
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What is resistance? |
The ratio of the voltage across a given component to the current in it. |
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Energy is lost across a resistor and other components.
What type of energy is lost across a resistor and what is it lost as? |
Electrical energy is lost across a resistor as heat. |
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What is the definition of Power? What are the 3 different equations used to calculate power? Give the units of power as well. |
Energy lost per second or work done per second. Power units: J/s or W (Watts) |
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Draw a current against voltage graph for a standard resistor. What is the gradient of this graph equal to? What does this resistor classify as and why? What is the relationship between current and voltage? |
Gradient = I/V = 1/R The resistor is Ohmic because the resistance is constant (straight lines have a constant gradient) Current (I) is directly proportional to voltage (V) |
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What is the circuit symbol for a lamp? Draw a current against voltage graph for a lamp. What is the gradient of this graph equal to? What is happening to Resistance (R) as voltage increases and why? |
Gradient is 1/R R increases as V increases because the filament in the bulb heats up. This heating up is caused by the increased current, causing the electrons to collide more with the vibrating metal ions in the filament. The increase in resistance is also shown on the graph. Since the graph gets more shallow as voltage rises, resistance rises as well since grad = 1/R. |
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Thermistors and light-dependent resistors (LDR) have the same current-voltage graphs. Heat is just interchangeable with light. Draw their current against voltage graph when the light/heat is: High Low. Label which graph represents which one. The gradient is still 1/R. What will happent to the resistance if heat/light is: High Low? Are these graphs ohmic? |
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Draw the current-voltage graph for a diode or light emitting diode (LED). what are the circuit symbols for a diode/LED? Label on what parts of the grsph resistance will be: High Low. At what voltage does current start to flow through a diode? |
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Draw a graph that shows how the resistance of an LDR varies with light intensity. Label which end represents dark and which end represents light. |
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Draw a graph that shows how the resistance of a thermistor varies with temperature. Label which end representd very hot and which end represents cold. |
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For resistors in series, how do you calculate the total voltage using the voltages through the resistors? How do you calculate the total resistance using the resistances that are given?
What is happening to the voltage? What is happening to the current? What would the ohms law equation be in this situation? |
V total = V1 + V2 +... R total = R1 + R2 +...
The voltage is being shared between each component (resistor). Current is the same throughout the whole circuit. V(total) = I x R(total) |
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Draw a circuit with 2 resistors in parallel and 3 ammeters. 1 in series with the 1st resistor before the circuit branches off, the other in series with the 1st resistor after the branch off, and the last one in series with the 2nd resistor. Label which ammeter shows the total current. |
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Components that are parallel to each other have the same what? |
Voltage (V) |
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When two components are parallel to each other, what happens to the current of the circuit? |
The current is shared between branches. |
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In this parallel circuit, how would you find: The current through R1?
The current through R2?
The total resistance?
The total current? (If it isn't given) |
Current through R1: I1 = V / R1
Current through R2: I2 = V / R2
Total resistance: 1/R(total) = 1/R1 + 1/R2 Then solve for R(total)
Total current: I(total) = V/R(total)
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In series, how do you find total resistance? |
R1 + R2 +... |
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In parallel, how do you find total resistance? |
1/R(total) = 1/R1 + 1/R2 +... Then solve for R(total) |
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A man named Kirchoff made laws for circuit. What is Kirchoff's 1st law? Give an example of this law using the diagram above. |
Kirchoff's 1st law: The total current entering a junction is equal to the total current leaving the junction. E.g. In the circuit above, A(total) enters a junction and splits into A1 and A2. Both A1 and A2 both leave their branches and meet at the same junction again. They add to form A(total). |
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What is Kirchoff's 2nd law? |
The sum of all voltages around any closed loop in a circuit must equal zero. |
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Practice question: Look at the circuit above. Find the total current in the circuit. |
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What is a Superconductor? |
Superconductor: A material that has no resistance below a certain temperature specific to it, also known as it's critical temperature. |
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What is a Potential Divider? |
Potential Divider: a combination of resistors in series connected across a voltage source to produce a required p.d. |
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Draw an example of a potential Divider.
This divider has a 12V voltage source, 2 resistors in parallel (1st one is 4 ohms, 2nd one is 2 ohms) and voltmeters connected in parallel to each resistor. |
The 12V could also be at the ball on the opposite end of the 0V, then remove the wire and cell between the 12V's new position and the 0V's position. |
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If the resistors had the same resistance, how much voltage would each resistor get and why? Since the resistors have different resistances, which resistor gets more voltage and why? |
If the resistors had the same resistance, they will get 6V each because they will get the same share of the voltage The 4 ohm resistor gets more voltage because the resistor with the BIGGER resistance will get a greater share of the voltage. |
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For potential dividers, what is the general equation that can be used to find the voltage (Vn)? (A voltage you are looking at) |
n is used to identify voltage/resistance you are looking at.
A resistor of Rn ohms has a voltage Vn volts go across it. |
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Find V2 using the information given to you. |
V2 = 4V |
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Potential dividers have real life applications. For example, heaters can use potential dividers to work. Where can we attach a heater in this circuit to ensure the heater turns on when it gets cold and why? Explain fully. |
Connect the heater in parallel to the thermistor. Explanation: - When its colder, resistance of thermistor↑ - If resistance increases, the thermistors share of the voltage ↑ too. - If something is connected in parallel to a component, it will receive the same voltage as the component. (E.g. Voltmeter in parallel to a resistor, voltmeter will read voltage given to the resistor) - If the heater is connected in parallel to the thermistor, it will receive a higher voltage as well, Allowing thr heater to turn on. |
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Fans can use potential dividers to work. Where can we attach a fan in this circuit to ensure it turns on when the weather gets hot? |
Attach it in parallel to the normal resistor. Explanation: - When its hotter, resistance of thermistor ↓ - If its resistance falls, the thermistors share of the voltage ↓ too. - The other resistor will receive more of the voltage, so the fan will receive that voltage as well, since its in parallel. The fan will turn on. |
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Street lights that turn on in the dark use potential dividers to work.
In this circuit, where would you attach a bulb to ensure the light turns on when it gets dark and why? Explain fully. |
Attach the light in parallel to the LDR.
Explanation: - Resistance of LDR ↑ when its darker.
- LDR gets a greater share of the voltage, V.
- the Light is connected in parallel to the LDR, so the light will receive the same voltage, making it turn on. |
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Besides as resistors and components, wires themselves can have resistance as well. What 3 things does the resistance of a wire depend on, and how would each factor affect the wire's resistance if they were increased? |
The resistance of a wire depends on: - It's length (Longer wire, higher R) - It's cross sectional area (Larger cross sec area, Lower R) - The wire's resistivity (p). (Larger resistivity, higher R) |
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What is the definition of resistivity? (Its definition is just the equation for resistivity). State what each part of the equation means. |
p is resistivity of wire R is resistance of wire A is cross sectional area of wire L is length of wire. |
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Explain how the resistivity of a wire can be found experimentally using results and a graph. |
Plot a graph of R (resistance of wire) against L (length of wire). Change L and measure R at each length. How to find R at each length: Do V/I for each length. The results should give points that form a straight line as their line of best fit. From this, p (resistivity) can be found by doing:
p = gradient x A (wire cross sec area). |
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In this circuit, a voltmeter is attached in parallel to a cell. The voltmeter will measure the terminal pd. 1) What is the definition of terminal pd? What is the terminal pd in this circuit? 2) The cell may produce 6V, but only 5.8V is read on the voltmeter. What is the reason for this? |
1) Terminal pd - the total pd of the circuit. Terminal pd = 5.8V 2) This is because some of the 6V is being lost in the battery BEFORE it even enters the circuit. Some of the voltage is lost in the battery because the battery has an internal resistance. |
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What is emf (electromotive force)? |
The total voltage in a circuit plus the voltage lost across the battery's internal resistance. |
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Draw a circuit where you can see the inside of the cell. Label where the internal resistance is. Add an ammeter and standard resistor in series to the circuit. |
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What is the equation used to calculate emf? State what each part of the equation means. |
Epsilon = emf I = total current in circuit R = total resistance of circuit (NOT including internal resistance) r = internal resistance of cell or battery. |
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Explain how you can find the emf of a battery and internal resistance of a battery experimentally. Include a graph. |
Connect a voltmeter in parallel to a cell/battery in a circuit.
Plot terminal pd (pd in the circuit) against current in the circuit. Start off with the current being high.
To decrease the current, increase the outside (variable) resistance (resistance that IS NOT internal resistance) in the circuit. Change current, measure terminal pd.
Gradient = -r (-ve internal resistance) Grad x -1 = r
Y intercept = epsilon (emf)
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What is Kirchoff's 1st law? Draw a visual example of the 1st law and briefly explain what is happening. |
The total current entering a junction is equal to the total current leaving the junction. E.g. look at image. I1 and I2 are entering the junction. They add to make I3. I1 + I2 = I3. |
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What is Kirchoff's 2nd law? |
The sum of all voltages around any closed loop must equal zero. (Basically, Total emf from cell or battery = sum of voltages lost to components in a closed loop. |
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In this circuit there are two loops. Loop 1 and 2, represented by the swirly arrows. (Not sure if the whole thing can be considered a loop yet) Using Kirchoff's 2nd law, write 2 equations. 1 for finding (epsilon)1 and the other for finding (epsilon)2. Write them in both V and IR forms, (Since V = IR) |
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Practice question: Look at this circuit. Using Kirchoff's 1st and 2nd laws, find I1, I2 and I3. (1st part of working out is on hint flashcard) |
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For cells in series, how do you find the total voltage if? a) the cells are connected in the same direction b) the cells are connected in opposite directions? |
a) add voltages b) subtract voltages |
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A variable potential divider may look something like this. In this case, it's being used for a light bulb. How can you increase the resistance of the resistor, thus increase the brightness of the bulb? How can you decrease the resistance of the resistor, thus decrease the brightness of the bulb? |
Increase: Slide the arrow thing (unsure of what its called. I think it's a wire) upwards. Decrease: Slide the arrow thing (unsure of what its called. I think it's a wire) downwards. |
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For identical cells connected in parallel, (They are all cells, you can just see their inside) what is the equation for the pd lost in (or the pd across the internal resistor of) each cell? (This one is on hint card) So how would you find the terminal pd produced from each cell? |
r is internal resistance I is total current supplied by the cells r is internal resistance of the cells. |
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You can find the potential difference between two wires.
How? |
Find the pd through wire 1 (see if any pd is lost due to resistors or components etc. Pd on wire left of resistor will be different to Pd on wire right of resistor )
Same for wire 2
Subtract the pd through each one by each other.
Done! |
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