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Flashcards in Required Practicals Deck (25)
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1

Describe the experiment used to calculate the specific heat capacity of a material:

-choose material and measure its mass
-wrap insulation around material
-smear petroleum jelly around the blub end of the thermometer
-measure starting temperature of material
-put heater in material with ammeter and voltmeter connected
- turn power pack on and start timing
- record ammeter and voltmeter readings every 60 seconds. Record temperature at same intervals too.
- turn off power pack (10 mins) and record highest temp
- calculate power of heater and then energy transferred at each time interval
- plot temp change (y) to energy transferred (x) graph

2

How do you calculate the specific heat capacity of the material using the temp change/energy transferred graph?

c = 1/(mass x gradient)

3

Why is it important to stir water regularly when heating?

To allow an even distribution of thermal energy throughout the volume of water

4

Why is petroleum jelly used on the bulb end of the thermometer?

To provide good thermal contact between the block and thermometer for accurate reading

5

What happens if the heating element is not in contact with the metal block?

-There is a layer of air between the heating element and block
- Dissipation of energy to internal energy store of surroundings
- Calculated specific heat capacity may be greater than the actual value

6

Describe the experiment which investigates the effect of layers of insulation:

- Set up beakers with different layers of insulating material around them
- Pour hot water into beakers
- Use cardboard with hole for thermometer as lid for beakers
- Put thermometers through holes and into water
- Measure start temp of water and then every five minutes
-Record measurements
-Continue for 20 minutes
- Plot cooling curve (temp/time)

7

Whats the conclusion to be drawn between heat loss and number of layers of insulating material?

-Greater the number of insulating layers
- lower the rate of thermal energy transfers

8

Why do many layers of insulating material prevent something cold heating?

- Many layers trap air between them
- Air has low thermal conductivity
- Reduces the rate of thermal energy transfer

9

Describe the method to investigate how the length of wire affects resistance discussing the preventtion of overheating and improving accuracy of results:

- Measure the length of wire (connected in circuit) using a metre rule
- Use a low value p.d. to avoid large current which will mean wire gets hot
- Temperature affects resistance so it must be controlled as far as possible
- Record the ammeter and voltmeter readings
- Divide the voltmeter reading by the ammeter reading to get the resistance of the wire
- Open the switch between measurements to prevent wire overheating
- repeat procudure for 10 different lengths of wire connected between (X) and (Y)
- Use the full range of lengths of wire
- repeat measurements for same lengths of wire
- keep wire tight to improve accuracy of measurements
- check data for anomalous results, repeat experiment if anomalies identified
- calculate the mean of the two resistance values for each length to minimise the effect of random errors

10

Describe the method to investigating resistors in series and in parallel:

- Set up battery, with ammeter and two resistors in series with a voltmeter in parallel to both resistors
- Turn on power pack at 4V
- Measure p.d. across power pack
- Measure p.d. across each resistor and current through them
- Calculate total resistance of circuit with resistors in series
- Repeat steps for resistors in parallel
- Calculate total resistance of the circuit with resistors in parallel
- Use R = V/I

11

Describe the relationship between the length of a wire and its resistance:

The length of a wire is directly proportional to the resistance of the wire

12

What happens to the current as the resistance increases?

Current reduces

13

How does adding a bulb to a circuit stop the wire from overheating?

- Because it increases the resistance
- thus reduces the current
- and the current has the heating effect

14

Describe how you would calculate the density of a regular shaped object:

- Measure length, width and height of obhject using ruler
- calculate volume using volume = length x width x height
- measure mass ofobject using balance
- calculate denity of object using density = mass/volume

15

Describe how you could calculate the density of an irregular shaped object:

- part fill beaker with water and measure the volume
- place object in water
- measure new volume
- calculate the volume change/ water displacement
- this is the object's volume
-measure mass of object using balance
- calculate density of object using density = mass/volume

16

Describe how you could calculate the density of a liquid:

- measure mass of empty measuring cylinder
- fill measuring cylinder with liquid
- measure the volume of liquid
- measure the mass of the measuring cylinder wuth the liquid
- calculate the mass of the liquid by calculating the difference between the two mass measurements
- calculate the density of the liquid using the formula: density = mass/volume

17

How do you calculate the resistance of a component from an I/V graph?

-Calculate the gradient
- Resistance = inverse of gradient

18

How do you keep a circuit at a constant temperature whilst taking I/V readings?

-Turn off the power supply between readings

19

Describe how to use a circuit to investigate how current through a diode affects the resistance of the diode:

- Use ammeter to measure current
- Use voltmeter to measure the potential difference
- Alter the resistance of the variable resistor to change current in the circuit or change p.d.
- Take recordings at varying currents
- Plot a current(y) against potential difference (x) graph
- Calculate resistance of diode from pairs of points on the graph, using R = V/I
-calculate resistance for large enough range of currents

20

What components are required to measure I/V characteristics with a resistor?

-Battery
-Variable resistor
-Ammeter
-Resistor
-Voltmeter(parallel)

21

What components are required to measure I/V characteristics with a filament lamp?

-Battery
-Variable resistor
-Ammeter
- Filament lamp
-Voltmeter(parallel)

22

What components are required to measure I/V characteristics with a diode?

-Power pack
-Variable resistor
- Ammeter
- Resistor
- Diode
-Voltmeter(parallel)

23

What should be on each axis for the graph plotting the relationship between resistance and length of wire?

X-axis : length of wire
Y-axis : resistance

24

What are the main features of a graph which show a directly proportional relationship?

-Line of best fit is a straight line
- that passes through the origin (0,0)

25

How are resistance changes deduced from an I/V graph?

- Shown by changes in gradient
- An increasing gradient indicates the resistance is decreasing
- A decreasing gradient indicates the resistance is decreasing