Required Practicals Flashcards

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1
Q

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

A
  • 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
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2
Q

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

A

c = 1/(mass x gradient)

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3
Q

Why is it important to stir water regularly when heating?

A

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

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4
Q

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

A

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

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5
Q

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

A
  • 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
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6
Q

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

A
  • 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)
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7
Q

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

A
  • Greater the number of insulating layers

- lower the rate of thermal energy transfers

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8
Q

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

A
  • Many layers trap air between them
  • Air has low thermal conductivity
  • Reduces the rate of thermal energy transfer
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9
Q

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

A
  • 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
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10
Q

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

A
  • 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
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11
Q

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

A

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

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12
Q

What happens to the current as the resistance increases?

A

Current reduces

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13
Q

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

A
  • Because it increases the resistance
  • thus reduces the current
  • and the current has the heating effect
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14
Q

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

A
  • 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
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15
Q

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

A
  • 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
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16
Q

Describe how you could calculate the density of a liquid:

A
  • 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
Q

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

A
  • Calculate the gradient

- Resistance = inverse of gradient

18
Q

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

A

-Turn off the power supply between readings

19
Q

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

A
  • 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
Q

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

A
  • Battery
  • Variable resistor
  • Ammeter
  • Resistor
  • Voltmeter(parallel)
21
Q

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

A
  • Battery
  • Variable resistor
  • Ammeter
  • Filament lamp
  • Voltmeter(parallel)
22
Q

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

A
  • Power pack
  • Variable resistor
  • Ammeter
  • Resistor
  • Diode
  • Voltmeter(parallel)
23
Q

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

A

X-axis : length of wire

Y-axis : resistance

24
Q

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

A
  • Line of best fit is a straight line

- that passes through the origin (0,0)

25
Q

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

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