Mechanics
1) Timing oscillations
(a) Disturbance due to wind can be avoided by switching off the fans and closing windows and doors.
(b) Ignore the first few oscillations and started timing only when oscillations were steady.
(c) Make sure that the angle of swing is small during timing (less than 5°).
(d) Measure the length of the pendulum from the point of suspension to the centre of the bob.
(e) When the oscillations of the pendulum become elliptical, reject the timing.
2) Parallax Errors
Whenever there is a gap between the scale and the mark to be read, parallax error is present.
(a) When reading the measuring cylinder or thermometer - parallax errors can be minimised by viewing the reading at eye-level and at the meniscus.
(b) When reading meteres such as voltmeter, ammeter, etc - parallax errors can be minimsed by viewing the pointer from directly above such that the pointer coincided with its image.
3) When judging whether apparatus is horizontal or vertical,
(a) Make use of the vertical edge of a door, blackboard, a wall or a plumbline to judge whether apparatus is vertical or not.
(b) Use the teachers' bench or the horizontal edge of the blackboad to judge whether or not your apparatus is horizontal.
(c) Also use a level when available
Heat
When working with heat ensure that:
1) The water or liquid in the vessel should be stirred constantly during the experiment so that the temperature is uniform throughout the water. (Note: Do not use the thermometer as a stirrer)
2) Do not place the thermometer at the bottom of the beaker when the water is being heated. This is because the temperature of the beaker is usually higher than that of water. Overheating may lead to over-expansion of the mercury thread resulting in a wrong reading and in some cases breaking the thermometer.
3) Temperature readings should be taken only when they are steady.
4) When comparing heat loss due to a change, e.g. the colour of the cooling vessel, make sure that all parameters remain the same except for the colour of the vessel.
(Make sure that starting temperature for both experiments are the same.)
5) Disturbance due to wind was avoided by switching off the fans and closing windows and doors.
6) Covered with a lid where possible to reduce heat loss by convection,
7) Perform experiment in good insulating material such as a styrofoam cup to minimise heat loss by radiation and conduction. Also lining the container with good insulating material such as cotton or wool can help to minimise heat loss.
Light
1) Using pins
(a) the pins should placed vertically upright. (Check with protractor or set-square.)
(b) the pins used to locate the path of a light ray should be placed more than 6 cm apart to minimise errors. (Check that pin-pricked points are clearly marked and labelled)
(c) Use the view from the base of the pins when aligning pins in a straight line as the pins may not be perfectly upright.
2) Using lenses
(a) Object and image distances should not be measured along a line parallel to the principal axis. A set-square can be used to minimise parallax errors.
(b) The lens must be upright and parallel to the screen.
(c) The illuminated object should be placed at the same height as the optical centre of the lens.
Electricity
1) Main
The meters (voltmeter and ammeter) must be read with the eye directly above the pointer such that the image of the pointer in the mirror cannot be seen, to avoid parallax error.
2) The contacts between the wires and the components and the plug of the switch must be tightened* to reduce contact resistance in the circuit.
(* This can be checked by shaking/tapping the connecting wires lightly at each part of the circuit and observe the ammeter's reading. If the reading fluctuates, it means there is a bad connection in the circuit.)
3) Make sure there is no 'kink' in the bare resistance wire especially when you have to measure the length of the wire accurately.
4) The jockey should be held vertically so that the readings obtained are more precise. Do not exert too much pressure on the resistance wire, otherwise the cross-sectional area will no longer be uniform.
5) Switch on the circuit for a few seconds before taking a reading and then switch it off immediately. This is to avoid unnecessary heating in the resistance wire as a change in temperature can affect the resistance.
Note: If you find that the connecting wires are not long enough, do not join up two pieces of wire. The contact resistance at the joint can be quite significant. Instead, ask for a longer piece of wire.