P2: Electricity Flashcards Preview

Physics GCSE Y11 > P2: Electricity > Flashcards

Flashcards in P2: Electricity Deck (79)
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1

What is potential difference?

Energy transferred per unit charge.

2

What is charge flow?

The total charge which has passed through a circuit in a given time.

3

What is the unit for charge flow?

Coulombs (C)

4

What is resistance? What causes it?

Something that opposes flow of charge, transferring energy away as heat.

Caused by electrons colliding with each other and the wire.

5

What is the unit for resistance?

The ohm (Ω).

6

What is power and its unit and symbol?

Rate of energy transfer to charges. Unit = watts (W); symbol = P.

7

What is current?

Rate of flow of charge.

8

What equation links voltage, current and resistance?

V = IR

9

What equation links current, time and charge flow?

Q = It

10

What equation links energy, voltage and charge flow?

E = QV

11

The length of a wire is directly proportional to its what?

Resistance.

12

Describe how you would investigate how wire length affects resistance.

• Connect an ammeter in series with a test wire, using crocodile clips to attach the wire to the test wire. Connect a voltmeter in parallel to the test wire.

• Place the 0cm mark on a metre ruler level with one clip, and attach the other clip a set distance away, recording the length of the wire between the clips.

• Record the current through the wire (ammeter) and pd across it (voltmeter).

• Open the switch and move the 2nd clip further down the metre ruler, again measuring the length between clips. Repeat step 3 with several different wire lengths.

• Turn off the circuit between readings to stop the wire heating.

• Use R = V/I to calculate the resistance for each length of wire, then plot the wire length against resistance. The graph should show a directly proportional relationship.

13

A student used the following method to investigate how wire length affects resistance:

• Connect an ammeter in series with a test wire, using crocodile clips to attach the wire to the test wire. Connect a voltmeter in parallel to the test wire.

• Record the length of the wire between the clips.

• Record the current through the wire (ammeter), and the pd across it (voltmeter).

• Repeat step 3 with several increasing wire lengths.

State the independent, dependent and control variables for this investigation.

Vind = length of wire (use metre ruler w/ mm intervals)

Vdep = resistance (calculated w/ current, pd)

Vcon = temp. of wire (turn off circuit between readings), type and diameter of wire, pd of cell/battery, other components kept the same.

14

A student used the following method to investigate how wire length affects resistance:

• Connect an ammeter in series with a test wire, using crocodile clips to attach the wire to the test wire. Connect a voltmeter in parallel to the test wire.

• Record the length of the wire between the clips.

• Record the current through the wire (ammeter), and the pd across it (voltmeter).

• Repeat step 3 with several increasing wire lengths.

Suggest how they could improve the validity of their results.

Use a metre ruler with mm intervals to increase the accuracy of length readings.

• Turn off the circuit between readings to prevent the wire from heating, which would affect its resistance.

• Take several readings for each wire length, omitting any anomalies and calculating an average.

15

How do circuits work?

1) Current flows clockwise from the negative side of the cell. 2) This side releases electrons, which push away electrons further down the wire. 3) At the other end of the circuit, the electrons are attracted to the positive end of the cell. 4) The space they leave causes electrons behind them to be attracted to the positive ions there.

16

How do cells work?

1) Chemicals in the negative end react to release electrons. 2) In the positive end, chemicals react to take in electrons.

17

1) Why do non-rechargeable cells run out? 2) How do rechargeable cells not run out?

1) In non-rechargeable batteries, the chemicals are used up, disrupting the electron flow. 2) Rechargeable batteries use chemicals that have reversible reactions.

18

How is pd shared in series circuits?

Shared between components, according to the ratio of resistance of these components.

19

How is current shared in series circuits?

Current is the same everywhere as there’s only one path for electrons to take.

20

How is resistance shared in series circuits?

The sum of all the resistors' resistances amounts to the total resistance. Resistors share the potential difference. The bigger a component’s resistance, the bigger its share of the pd.

21

Describe how you could investigate the effect of adding identical resistors to a series circuit's total resistance.

• You'll need mimimum 4 identical resistors.

• Assemble a series circuit, including one of the resistors and an ammeter.

• Measure the current (ammeter) and calculate the resistance using Ohm's law, R = V/I. (pd = pd of battery.)

• Add another resistor in series, and repeat the same steps, measuring the current and calculating the resistance.

• Repeat step 4 until you've added all the resistors.

• Plot the number of identical resistors against the total resistance of the circuit (relationship will be proportional).

22

How is pd shared in parallel circuits?

Pd is the same across all branches because components are not having to share it, like in series.

23

Compare the brightness of identical bulbs connected in parallel.

They will be at the same brightness.

24

How is current shared in parallel circuits?

It diverges. The current of each branch adds to make the total current. If identical components are connected in parallel, the same current will flow through each branch.

25

How is resistance shared in parallel circuits?

Total resistance is always smaller than the resistance of the smallest resistor. Adding a resistor in parallel decreases the total resistance, because fewer electrons pass through each resistor, making it easier for each one to pass through.

26

What effect does adding a resistor in parallel have?

It decreases the total resistance, because fewer electrons pass through each resistor (an extra branch has been added). Since V = IR, and V is constant in parallel circuits, when the resistance decreases, it causes an increase in current on each branch.

27

In a parallel circuit, as you add identical resistors in parallel to one another, the resistance __.

Decreases.

28

Describe how you could investigate the effect of adding identical resistors to a parallel circuit's total resistance.

• You'll need mimimum 4 identical resistors.

• Assemble a series circuit, including one of the resistors and an ammeter.

• Measure the current (ammeter) and calculate the resistance using Ohm's law, R = V/I. (pd = pd of battery.)

• Add another resistor in parallel to the first; repeat the same steps, measuring the total current and calculating the resistance.

• Repeat step 4 until you've added all the resistors.

• Plot the number of identical resistors against the total resistance of the circuit. The resistance will decrease with no. resistors (but not proportionally - see graph).

29

Describe how you could investigate how the pd through a filament lamp affects its current.

• Attach in series a variable resistor, ammeter, and bulb, and a voltmeter in parallel with the bulb.

• Take current readings with the ammeter as you alter the pd across the bulb (measured with the voltmeter) using the variable resistor.

• Turn the circuit off between readings to stop the wire heating up.

• Plot the pd (independent variable) against the current (dependent variable) on a graph.

• Control variables: component under investigation, type of wire, cell/battery and other components.

30

What are ohmic conductors?

Components which follow Ohm's law (V=IR). This includes wires and resistors. Their resistance is constant and doesn't vary with current.