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PHYSICS A LEVEL REVISION - LVI > Practical Skills (CPACs 4, 5, 8) > Flashcards

Practical Skills (CPACs 4, 5, 8) Flashcards

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1
Q

Defnine Young’s Modulus.

A

A ratio of tensile stress to tensile strain and measures the stiffness of a material

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2
Q

How is stress calculated?

A

Stress = Force / Cross-sectional Area

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3
Q

How is strain calculated?

A

Strain = Change in Length / Original Length

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4
Q

What is the unit of stress?

A

Pascals, Pa or Nm^-2

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5
Q

What is the unit of strain?

A

It is unites as it is a ratio of two lengths

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6
Q

What is the unit of Young Modulus?

A

Pascals, Pa or Nm^-2

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7
Q

How can the cross-sectional area of a thin wire be measured?

A

The diameter can be measured using a micrometer in several places along the wire. The average diameter can be used to find the area using A = (pi x d^2) / 4

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8
Q

What safety precautions should be taken when stretching thin wires?

A

Safety goggles should be worn as the wire may snap causing damage to eyes

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9
Q

Why should the temperature of the surroundings be kept constant when carrying out this experiment?

A

Metals undergo thermal expansion when there is a temperature increase, altering the dimensions of the wire

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10
Q

Why should a pre-stress be applied to the wire when setting up this experiment?

A

So that all kinks in the wire are removed and the wire is taut before measurements are taken

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11
Q

How can the Young Modulus be determined from a graph of extension against load?

A

The gradient, G is ΔL / F

E = L / (G x A)

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12
Q

Suggest what has happened if the length of wire doesn’t return to its original length when unloaded.

A

The load may have exceeded the wire’s elastic limit so the wire has undergone plastic deformation

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13
Q

How can the load applied on a wire be calculated from the mass added to the end of the wire?

A

F = m x g

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14
Q

What safety precaution should be taken when using hanging masses?

A

Never stand with your feet below the hanging masses incase they fall, place a padded bucket or sand tray below them to catch them in the event that they fall

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15
Q

Suggest how the extension of the wire may be measured.

A

A marker like a piece of tape can be added to the wire. Place a metre rule under the wire, allowing the movement of the marker to be measured

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16
Q

Why is the choice of wire diameter important to obtain successful results?

A

If the diameter is too large the extension of the wire will be too small to measure accurately. If it is too small, the wire may deform plastically before a suitable range of data has been collected

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17
Q

Suggest why a comparison test wire is used when conducting this experiment using Searle’s apparatus?

A

A comparison wire is included so that any changes in the environmental conditions (eg change in temperature) are accounted for

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18
Q

Why is the choice of wire length important in the experiment?

A

The length needs to be large enough that extension is sufficiently measurable

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19
Q

Suggest how the wire may be fixed in place when carrying out the experiment.

A

The wire can be clamped tightly between two blocks of wood at one end. These blocks can then be clamped to the bench or beam

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20
Q

Alongside a metre rule, what other instrument can be used to measure extension accurately?

A

A set-square can be used to help read the extension accurately

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21
Q

When measuring the diameter of the wire in multiple places, why should you rotate the wire between measurements?

A

The different orientations ensure the wire is circular across the full length of the wire

22
Q

State the equation used to calculate the resistivity of a wire.

A

p = RA / L

23
Q

How does the resistance of a wire change when the cross-sectional area decreases?

A

The resistance of a wire is inversely proportional to the cross-sectional area, so as area decreases the resistance increases

24
Q

How does the resistance of a wire change when the length is decreased?

A

The resistance of a wire is directly proportional to the length of the wire, so as the length decreases the resistance also decreases

25
Q

How does the resistance of a wire change if the resistivity is increased?

A

The resistance is directly proportional to its resistivity, so as resistivity increases the resistance increases

26
Q

What is the unit of resistivity?

A

Ωm

27
Q

How do you find the cross-sectional area of a thin wire?

A

Using a micrometer, measure the wire’s diameter at three places along the sure and input the average diameter into the circular area equation

28
Q

Suggest how the length of conducting wire can be varied when carrying out this equation.

A

One end of the wire can be fixed and the other end can be connected to the circuit using a crocodile clip. The length of wire can be changed by moving the clip’s position

29
Q

What device is used to measure the potential difference across the wire and how is it connected?

A

A voltmeter which is connected in parallel across the wire

30
Q

What device is used to measure the current flowing through the wire and how is it connected?

A

An ammeter that is connected in series with the wire

31
Q

Why should the power supply be switched off between readings of the potential difference?

A

The temperature of the wire should remain constant throughout the experiment. Switching the power supply off between readings mitigates against heating of the wire

32
Q

Why should the temperature of the wire be constant throughout the experiment?

A

Temperature can impact the resistance of the wire so is therefore a control variable

33
Q

Why does resistance of a wire increase when its temperature increases?

A

As temperature increases, the metal ions gain more kinetic energy and vibrate more. These vibrating ions make it harder for change to pass through it, increasing its resistance

34
Q

How can the resistivity of a wire be determined from a graph of resistance against length?

A

The gradient, G is R / L so multiply G by the cross-sectional area, A gives the resistivity

35
Q

Why should the current in the wire be kept low?

A

As current increases, the temperature of the wire increases. Keeping the current low reduces the heating effect

36
Q

State Boyle’s Law.

A

When temperature is constant, the pressure of an ideal gas is inversely proportional to its volume, pV = constant

37
Q

State Charles’ Law.

A

When pressure is constant, the absolute temperature of an ideal gas is directly proportional to its volume, V / T = constant

38
Q

How would you measure the cross-sectional area of the inside of a syringe?

A

Remove the plunger and use a micrometer to measure the diameter of the seal. Submit this value into the circular area equation

39
Q

Why should the clip used to seal the tubing coming from the syringe be as close to the syringe tip as possible?

A

The volume of air trapped in the tubing should be as small as possible so that it is negligible in comparison to the volume of air in the syringe

40
Q

Suggest how a mass hanger could be attached to the plunger of the syringe.

A

A small piece of string can be tied to the plunger to form a loop. The hanger can then hook onto this loop

41
Q

Why should the syringe be clamped above the region of the plunger’s motion?

A

Clamping the syringe can distort the barrel and hinder the motion of the plunger. This also ensures that the scale can be accurately read

42
Q

Why should the syringe be clamped at a relatively high position?

A

The syringe should be clamped at height so that the plunger can move freely as masses are added

43
Q

How can the force exerted by the masses be calculated?

A

F = mg

44
Q

How can the pressure exerted by the masses on the air sample be calculated?

A

Pressure = Force / Cross-sectional Area

This is then subtracted from the standard atmospheric pressure

45
Q

State the value of standard atmospheric pressure.

A

101 kPa

46
Q

Describe the relationship that should be found when a graph of 1/V against P is plotted.

A

Pressure and volume are inversely proportional so the graph of 1/V against P should be a straight line that passes through the origin

47
Q

Suggest what a straight line may not be produced when plotting a graph of 1/V against P.

A

The plunger may have experienced some resistance to its motion as masses were added

48
Q

What safety precautions should be taken when using concentrated sulphuric acid?

A

Safety goggles should be worn to ensure no acid enters the eyes, gloves can also be worn

49
Q

What safety precautions should be taken when working with a hot beaker of water?

A

Avoid touching it with bare hands, and place a heatproof mat under it

50
Q

What should you do before recording each measurement of water temperature?

A

You should always stir the water before taking a temperature measurement so it is accurate

51
Q

Explain how an estimate of absolute zero can be obtained from a graph of length of air samples against temperature.

A

The graph will be in the form L = mθ + c

Sub in values from the graph to get c, then rearrange for θ when L=0 to find absolute zero

PHYSICS A LEVEL REVISION - LVI (9 decks)

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