Paper 6 Notes

Safety Precautions Many questions will ask about minimising risks here are the most common things: – Live wires should not be touched (electricity) – Hot objects should not be touched with bare hands – gloves should be worn – Circuit connections should be checked before switching on the power supply. – While changing components (resistors etc.) the power supply should be turned off to stock electric shocks – Safety goggles and gloves to be worn where relevant (e.g. hookes law)

Common Practicals

Centre of Mass Apparatus :- 2D object (Plane lamina) Procedure :- 1.Make a hole in the object 2.Hang it so it can swing freely 3.Hang a plumb line at the same point and mark a line through where it passes. 4.Repeat twice to get more lines 5.Where they intersect is the centre of mass. Stability :- The lower the centre of mass is the more stable an object is

Improving Accuracy General :- – Repeat the experiment 3 times to calculate an average reading. – To avoid parallax error, look perpendicular to the ruler. – Always check for zero error if there are inaccuracies in measurement. Center of mass experiment :- – View the string from directly in front of the card.

Improving Accuracy Minimizing heating effect of current (resistance) :- – Lower current – Increase voltage – Add a lamp – Increase the resistance of a resistor How to check a rule really is vertical :- – Use a set square or protractor – Plumb line – Spirit level

Improving Accuracy Variables in experiments based on springs :- – Number of coils – Length of spring – Diameter\thickness of spring – Selection of loads Getting accurate readings of V and I :- – For I only: Limit current so that temperature doesn’t increase – For I and V: Switch off between readings.

Improving Accuracy Fair test for pendulums (Keep these constant) :- – Length of pendulum – Shape of bob – Number of swings – Amplitude (how far you pull back to release) Why we measure 10 oscillations rather than 1 :- – Reduce human errors – Gives a more accurate value of time taken (T) – Gives an average of T

Improving Accuracy Precautions and procedures in electrical experiments :- – Check for a zero error – Initially choose the highest range when using a multi- meter then reduce the range to get a more accurate result. – Check that connections are clean – Switch off current when not taking measurements – When measuring resistance use low current’s to avoid heating and changing the resistance

Improving Accuracy Why angle i is NOT equal to angle r in reflection :- – Thickness of mirror – Protractor is not precise Inaccuracy of ray box method :- – Thickness of rays

Improving Accuracy Drawing graphs :- – Label axis – Choose a suitable scale (even numbers, even spacing) – Well judged line of best fit (straight line or smooth curve) – Thin and neat lines Measuring the gradient :- – Draw a triangle on the graph (to make it obvious you’ve attempted) – Use clear lines – Triangle should be larger than half the line For 2 values to be directly proportional, the line must go through the origin