Here are some precautions to Improve Accuracy of an experiment (by topic):

Mechanics

1. Checking for horizontal and vertical alignments

• • Use a spirit level, or a plumbline and a set-square to check whether the apparatus or set-up is horizontal or vertical.
  • Measure both ends from the top of the bench to judge whether the apparatus or set-up is horizontal.
  • Make use of the edge of a door, blackboard, or a wall to judge whether the apparatus or set-up is horizontal or vertical.

2. Experiments involving oscillations

• • The angle of oscillation(for pendulum) should be small, not more than 10° so that the oscillations are regular.
  • Allow the pendulum to swing until the oscillations are steady before taking readings so as to obtain a regular period of oscillation.
  • Allow the pendulum bob swing for a few oscillations to ensure that it is along the vertical plane so as to obtain a regular period of oscillation.

3. Balancing moments

• • Check that the uniform stick/rod/ruler being used can be balanced at its mid-point (c.g.)
  • Check that the stick/rod/ruler is able to rotate freely about the balancing point or other pivots.

Optics

1. Using Optical Pins

• • Use a protractor or set-square to ensure that the pins are placed vertically upright.
  • The 2 pins that are used to locate the path of a light ray are placed more than 5.0 cm apart to minimise errors in the location of rays. (Do check that pin-pricked points are clearly marked and labelled).

2. Using Lenses

• • The lens must be place upright such that it is at right angles to the bench so that the object and image distances are measured along a line parallel to the principal axis.
  • The illuminated object should be placed at the same height as the optical centre of the lens so that its image will also be formed at the same level.
  • The screen should also be placed in a plane at right angles to the principal axis to capture a sharp image of the object.

Electricity

• • The contacts between the wires and all the components (e.g. battery, resistors, plug switch) in the circuit 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 poor connection in the circuit.)
  • Close the circuit only when you are ready to take readings and then open it immediately after taking the readings. This is to avoid the heating effect of the current which would cause a rise in temperature and affect the resistance in the circuit.

Thermal Physics

• • The water or liquid in the vessel must be stirred constantly during the experiment so that the temperature is uniform throughout.
  • Care must be taken to reduce the heat loss or heat gain through conduction, convection or radiation (if possible) to/from the surroundings.

 

Non-Examples

• The following are NOT accepted as precautions in answering a question in a practical:

1. Parallax error – you are expected to know how to use instruments properly. i.e you should be doing the following:

• • place the eye directly above / at eye level with the markings when taking readings from the scale (on the instrument) so as to avoid parallax error.
  • when taking reading for a volume of liquid, the eye must be placed at the same level as the meniscus of the liquid.
  • when reading analogue meters, parallax errors can be minimized by viewing the pointer from directly above such that the pointer coincides with its image.

2. Disturbance due to wind – this can be avoided by switching off the fans and closing the windows – this is an expected precaution to take!

 

Basics