Alternative to Practical

do in (lens)

do in a darkened room/use a brighter light

mark (lens)

position of the centre of the lens to ensure measuring to correct point (difficulty finding the centre may lead to inaccuracy in experiment)

adjust (lens)

screen backwards/forwards to achieve the best focus: move screen slowly (may be difficult to decide correct position (leads to inaccuracy))

fix (lens)

fix/clamp ruler to desk

align (lens)

object and centre of lens at same height

set (lens)

object, lens and screen must be perpendicular to bench

read (lens)

look perpendicular to ruler to make measurements, or make sure that ruler is touching the object, lens holder and screen

limit (lens)

distance between object and screen: if the focal length is F, then the closest you can form a real image is with object->lens

use (optics)

use of optical pins for refraction/reflection experiment (they tend to use this set-up rather than a ray box, as it can be done more accurately)

ensure (optics)

ensure pins are vertical and spaced far apart

draw (optics)

use thin pins / thin pencil lines when drawing lines between pins to make the measurement

view (optics)

view bases of pins

difference (springs)

difference between extension and length: you measure unstretched (original) length and stretched length – the difference (stretched length – original length) is the extension

HOW TO SOLVE PARALAX (springs)

parallax is commonly a problem – you might use a set-square (or pointer) to make sure that your position reading is taken parallel to the scale on the ruler

mark (cars/balls on ramps)

mark a line for start/end position

release (cars/balls on ramps)

release car/ball without pushing

time (cars/balls on ramps)

time from same point of car/ball

how to improve timing accuracy (cars/balls on ramps)

use light gates to improve timing accuracy

displacement (measuring density)

displacement in measuring tube (remember: measure volume before adding object, and after adding object. The difference is the volume)

what mass do you need (measuring density)

mass of object, object plus water etc.

source error (measuring density)

inaccuracy: water left in measuring cylinder, water left on object, water splashes out when object put in

wrap (measuring circumference)

wrap a string around several times, divide by number of turns

start at _ temp(cooling)

start at same temperature

room (cooling)

same room temperature

what affects the rate of cooling (cooling)

draughts/humidity/insulation/volume may affect rate of cooling

rate of cooling depends on diffrence between(cooling)

rate of cooling depends on difference between substance’s temperature and room temperature

make sure the thermometer is in _, not …. (cooling)

make sure thermometer is in liquid, not touching bottom

how to avoid parallax (cooling)

read thermometer perpendicular to reading to avoid parallax

cell can ___ (electrical experiments)

cell can run down during experiment (may make repeats different)

reading analogue meters - different readings may result from _____ (electrical experiments)

reading analogue meters – different readings may result from interpolating between marks

temperature (electrical experiments)

temperature change may affect resistance (e.g. resistor heating up)

draw___, using ____ (electrical experiments)

draw circuit diagrams carefully, using standard symbols (see page in syllabus