Flashcards in Required Practicals Deck (25)
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
How do you calculate the specific heat capacity of the material using the temp change/energy transferred graph?
c = 1/(mass x gradient)
Why is it important to stir water regularly when heating?
To allow an even distribution of thermal energy throughout the volume of water
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
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
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
-Continue for 20 minutes
- Plot cooling curve (temp/time)
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
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
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
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
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
What happens to the current as the resistance increases?
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
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
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
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
How do you calculate the resistance of a component from an I/V graph?
-Calculate the gradient
- Resistance = inverse of gradient
How do you keep a circuit at a constant temperature whilst taking I/V readings?
-Turn off the power supply between readings
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
What components are required to measure I/V characteristics with a resistor?
What components are required to measure I/V characteristics with a filament lamp?
- Filament lamp
What components are required to measure I/V characteristics with a diode?
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
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)