ATP Cheat Sheet
1.
Experiments in general physics
Measuring length
 To measure heights, the ruler must be held perpendicular to the base
 Fix the ruler to the bench
 Measure using the fiducial point of objects- take the distance from both sides and
then average it
 Avoid parallax position yourself opposite the measuring device
 Avoid zero error
Measuring volume
 Always read the value at lower meniscus
 Keep cylinder on a level surface at eye level
 Ensure the liquid level has stabilised before taking a reading
Sources of error in moments experiment
 The loads obscure the scale making it difficult to judge the centre position of the load
Factors for fair test in pendulum experiment
 Shape of bob
 Length of string
 Amplitude
 Number of swings
Variables to be kept constant when comparing extension of springs with different material
 Cross section of spring
 Length of spring
 Room temperature
Centre of mass of a plane lamina experiment
 Make a hole in the lamina
 Suspend it on a pin so it can swing freely
 Hang a plumb line against the lamina
 Mark the line it passes through
 Repeat for another line and the intersection point is the centre of mass
2. Experiments with heat
When using a thermometer

Check the level of immersion in the liquid, minimum 1/3 immersion is required for a
proper reading

Thermometer should not touch the walls of a beaker

Take reading at eye level to avoid parallax error

Wait until reading stabilises
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When comparing thermometers readings, both thermometers have to be at the same
height
Swirl the liquid before measuring to avoid getting inaccurate readings
General precautions

Choose volume/mass values of the quantities that give large changes in the
temperature

Insulate the container

Cover the container

Stir and wait for highest temperature after stopping heating

For Specific Heat Capacity experiments, the warmer the room temperature, lesser
energy will dissipate into surroundings

If more than one quantity is being measured, record temperature at same time

Ensure starting temperature is the same

Use insulating materials for container and all other apparatus

Room should not be windy/have any draught
How to obtain a large temperature difference
 Increase temperature of water
 Increase draught over surface
 Increase surface area
 Record data at longer time intervals
 Decrease room temperature
 Decrease volume of water
3. Experiments with light
State precautions you would take to get accurate results from an optics experiment:
 Dark room
 Object, lens and screen must be same distance from bench
 All components should be on a levelled and sturdy platform
 Each component should be of the same height and lie on the same optic axis
 Move lens back and forth slowly
 Use a translucent screen
 Use fiducial aid when measuring distance
 Repeat and take average of the results
 All components should be perpendicular to the surface
Why is it difficult, in optics experiment to decide the best position of the lens to obtain a
sharply focused image on the screen?:
 Image appears focused only for small range of lens positions
 Not all of the image is focused
Describe one difficulty that might be experienced when measuring height of image in the
optics experiment:
 Hand in way of image - use translucent screen and view from behind
 Fix ruler to screen - fix ruler to screen
What are precautions that need to be taken when doing the pins experiment:


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Use thin line
Pins must be at least 5 cm apart
View the bases of the pin
Ensure that the pins are vertical
Why angle of incidence is not same as the angle of reflection
 Lines are too thick
 Protractor isn’t precise
4. Experiments with electricity
A reading of 0.623V is obtained even when lamp is switched off. Suggest reason and how to
overcome:
 Ambient light - do experiment in complete darkness
 Zero error - subtract zero reading from each voltage measurement
Minimise temperature increase in a current carrying wire
 Use a smaller current
 Use a wire with lesser resistance
 Open switch between readings
General precautions
 Initially choose the highest range for the ammeter/voltmeter, then reduce the range for
the ammeter so that the deflection is almost full scale
 Always check polarities before closing the switch (completing the circuit)
 Always check that connections are clean.
5. Experiments with magnets
Procedures for measuring magnetic field:
 Ensure magnet is in the same orientation as earth's magnetic field
 When iron filings are spread near magnet, gently tap to find the field
 Move centre of compass along the line from the magnet
 Tap compass to prevent sticking
 Use a sharp pencil when marking the ends of needle with compass
 Look directly down the compass to avoid parallax error
6. How to answer a question
E - equation
C - change
O - other
R - repeat
M - measure
S - same