Chapter 0: Practical

Question 1

What are the sources of error for an electrical experiment?

Answer 1

• The wire becomes hot after some time thus changing the resistance of the wire. Hence, the values of I (or V, depending on experiment) recorded will be affected
• Cell may run down or power of cell may be less after some time. Hence, the values of (or V depending on the experiment) recorded will be affected.
• There are kinks on the wire and wire cannot be straightened on ruler. Thus, the measurements of L is innaccurate.
• There is no scale on the mounting board / bench and it is difficult to ensure that the ruler is parallel to the wire. Thus, the measurement of L is inaccurate
• The wires are not of uniform thickness thus resistance of the wire is not uniform. Hence, the readings taken at each point may not reflect the actual values.
• Contact of jockey is not consistent, causing some variations in the readings of V.

Question 2

What are the sources of error for a spring experiment?

Answer 2

• Difficult to align protractor and spring balance. Thus, the measurement of θ is inaccurate.
• The spring balances may not be exactly identical, making it difficult to ensure that the spring balances are suspended at the same angle.
• As the spring stretches, it may not be possible to find the same reference points for the measurement of L. The reference points are estimated and hence, the measurement of L may be inaccurate.

Question 3

What are the sources of error for a U-tube experiment?

Answer 3

• Water is colourless / transparent, thus making it difficult to read the exact values of h.
• The water level is not exactly in line with the scale thus the readings of d and h have to be estimated.
• It is difficult to ensure that the 30cm ruler held by hand, to measure the height of the liquid is steady and vertical.

Question 4

What are the sources of error for a moment / horizontal ruler experiment?

Answer 4

• The retort stand provided does not allow for small changes to the height, thus the metre rule may not be exactly horizontal. Hence, reading of L may be inaccurate
• Difficult to measure x as the string hanging the mass is too thick and covers the metre rule may not be exactly horizontal. Hence, reading of L may be inaccurate
• Ruler may not be uniform and the weight of the ruler is not evenly distributed / centre of mass is not at the centre of the ruler / is not exactly over the pivot

Question 5

What are the sources of error for a mirror experiment?

Answer 5

• The mirror is very light and shifts easily despite checks. This causes error in the angle of incidence and hence the emergent ray.
• Alignment of P3 to the images of P3 to the images of pins P1 and P2 may not be perfect / can only be estimated, hence values of y recorded will be inaccurate.
• Pin 1 is not exactly at the stipulated position due to the thckness of the pin; the pin cannot be placed at exactly the outline of the glass block and will introduce error in the positions of pins 2 and 3 and hence, the measurement of y.

Question 6

What are the sources of error for a lens experiment?

Answer 6

• In order to measure x, the ruler must be placed against the lens and thus the lens may be shifted.
• The centre of the lens holder may not be perfectly aligned with the centre of the lens. Hence, position of the centre of lens will not be at the correct, measurement of u and v would be inaccurate.
• Difficult to keep the position of observer’s eye fixed throughout the experiment.
• Sharpness of image can only be estimated. It is difficult to determine / judge that the image on the screen is at its sharpest. Hence image distance (v) measured will be inaccurate or Hence, focal length (f) measured will be inaccurate (distant object experiment)
• Difficult to make fine adjustment to the height of the boss (retort stand) to obtain the height x of the lens such that the separation between the lines seen through the lens appears to be exactly double. Hence, an inaccurate measurement of x will be obtained.

Question 7

What are the sources of error for a rolling-pin experiment?

Answer 7

Difficult to ensure that the starting position of the rolling pin is constant throughout the experiment. Thus, the time taken could be inaccurate.

Question 8

What are the sources of error for a oscillation experiment?

Answer 8

• Difficult to measure the length of the pendulum as it is difficult to determine the centre of mass of the bob
• Difficult to judge complete oscillation, making the reading for T inaccurate

Question 9

What are the sources of errors for a thermal experiment?

Answer 9

• Thermal energy is lost to the surrounding when transferring the slotted mass into the Styrofoam cup, thus the temperature T recorded may be lower than the actual value.
• Temperature throughout water may not be uniform because stirring is difficult with slotted mass in cup
• Some water from the beaker clings onto the slotted mass and increases, m, the mass of water in the cup.
• Thermal energy is lost to the beaker or surrounding, thus the measurement of T is inaccurate.

Question 10

What are the sources of error for a laminar experiment?

Answer 10

• The plumb line drawn is only estimated to be vertical / is not perfectly vertical as the paper tends to shift when marking. This causes the lines to be inaccurately drawn hence affecting values of x and y
• The holes created could be too big, causing a shift in CG, making the reading for x and y to be inaccurate

Question 11

What is the symbol and units for length

Answer 11

km, m, cm, mm

l, h

Question 12

What is the symbol and units for area?

Answer 12

m², cm²

A

Question 13

What is the symbol and units for volume

Answer 13

m³, cm³

V

Question 14

What is the symbol and units for weight

Answer 14

Newton, N

W

Question 15

What is the symbol and units for mass?

Answer 15

kg, g, mg

M, m

Question 16

What is the symbol and units for time?

Answer 16

h, min, s, ms

t

Question 17

What is the symbol and units for a period?

Answer 17

s

T

Question 17

What is the symbol and units for density

Answer 17

g/cm, kg/m

ρ

Question 18

What is the symbol and units for speed?

Answer 18

m/s

u, v

Question 19

What is the symbol and units for acceleration?

Answer 19

m/s²

a

Question 20

What is the symbol and units for acceleration of free fall?

Answer 20

m/s², N/kg

Question 21

What is the symbol and units for moment of force?

Answer 21

Nm, Newton-metres

Question 22

What is the symbol and units for work done?

Answer 22

J, Joules

W, E

Question 23

What is the symbol and units for energy?

Answer 23

J, Joules
kWh, kilowatt-hours

E

Question 23

What is the symbol and units for power?

Answer 23

W, watts | P

Question 24

What is the symbol and units for pressure?

Answer 24

Pa, N/m², mmHg | p, P

Question 24

What is the symbol and units for temperature?

Answer 24

θ | °C, K

Question 25

What is the symbol and units for heat capacity?

Answer 25

C

Question 26

What is the symbol and units for latent heat?

Answer 26

J | L

Question 27

What is the symbol and units for frequeny?

Answer 27

Hz | 𝑓

Question 28

What is the symbol and units for angle of incidence?

Question 28

What is the symbol and units for wavelength?

Answer 28

m, cm | λ

Question 29

What are the precautions to take for Mechanics experiment?

Answer 29

Some precautions that should be taken when** timing oscillations:** Avoid disturbance due to wind by switching off the fans, and closing the windows and doors time 20 oscillations, then find period by dividing answer by 20 to reduce error due to human reaction time. Ignore the first few oscillations and start the timing only when the oscillations are steady Make sure that the angle of swing is small when timing the oscillations. it should be ≤ 5° Ensure that the length of the pendulum is measured from the point of suspension to the centre of the bob. When the oscillations of the pendulum become elliptical, reject the timing. Do NOT release the bob with force. **Some precautions that should be taken when ensuring that a piece of apparatus is horizontal or vertical:** To determine whether the apparatus is vertical, use a plumb line To determine whether the apparatus is horizontal, use a spirit level.

Question 30

What are some precautions to take for thermal experiments?

Answer 30

Some precautions that should be taken when measuring temperature: Stir the liquid in the vessel continuously during the experiment so that the temperautr is uniform throughout the liquid. (Note: Do not use the thermometer as a stirrer, to avoid breaking it.) Do not touch the bottom of the vessel with the thermometer when the liquid is beaing heated. Contact between the thermomete and the bottom of the vessel may lead to overheating and over-expansion of the mercury thread, thus breaking the thermometer. Only take temperature readings once they are steady When investigating the difference in thermal energy due to the chnage of a particular variable, such as the colour of the cooling vessel, ensure that all other parameters remain unchanged among experiments. For example, ensure that the same starting temperature is used for all the experiments. Avoid disturbance due to wind by switching off the fans, and by closing the windows and doors (to claim that thermal energy loss is constant, external conditions= should be the same). Minimise parallax error when reading a measuring cylinder or thermometer by viewing the meniscus at eye-level (Parallax error should typically not be written; as a source of error) Some precautions that should be noted when using a calorimeter: Cover it with a lid to reduce thermal energy loss by convection Place it in a shiny jacket lined with good insultaitng material, such to minimise thermal energy loss by radiation and conduction

Question 31

What are some precautions to take for light experiments?

Answer 31

Some precautions that should be taken when using pins: The pins should be placed vertically upright. This should be checked using a protractor or a set-square. Place the two pins used to locate the path of a light ray far enough apart (e.g. more than 6 cm apart) to minimise error. Ensure that pin-pricked points are clearly marked and labelled. View the base of the pins when aligning them in a straight line, as th pins might not be perfectly aligned. Some precautions that should be taken when using lenses: Object, lens, and screen must be perpendicular to the bench by placing a set square perpendicular to the metre rule and along the surface of each side of the beaker to avoid parallax eror. Move screen slowly to and fro until sharpest focus obtained. Object and lens are the same height above the bench. Carry out the experiment away from other bright light sources or in a darkened room. To obtain a more reliable value of focal length, f: Vary the values of distance from opening to the lens to collect 6 sets of values of distance from opening to the lens and distance from lens to screen. Plot a graph of 1/v against 1/u. f can be found from the reciprocal of the y-intercept of the graph. To measure the thickness of the lens accurately: Place set square and lens vertically on the metrke rule, with the set squares at the thickest part of the lens. Read the metre rule valyes from the corners of the set square and the difference is the thickness of the lens.

Question 32

What are some precautions to take for electricity experiments?

Answer 32

Some precautions that should be taken when working with circuits: To avoid parallax errors, read ammeters and voltmeters with your eyes directly above the pointer, such that the image of the pointer in the mirror is directly under the pointer, and thus, cannot be seen. Tighten the contacts between the wires and the circuit components to reduce contact resistance in the circuit. Check by shaking or tapping the wires lightly at each connection in the circuit while observing the ammeter’s reading. If the reading fluctuates, then the connection is unstable. Ensure that there are no “kinks” in the resistance wire, especially if the length of the wire must be measured accurately. Hold the jockey vertically so that more precise readings are obtained. Do not exert excessive pressure or slide the jockey on the resistance wire, otherwise the cross-sectional area of the wire might no longer be uniform. Switch on the circuit just a few seconds before taking a reading and then switch it off again immediately after that. This helps to avoid unnecessary heating of the resistance wire, as a change in temperature can affect its resistance