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