Download Certificate Physics

Certificate Physics
Few Hints  Big Reward
edited by King Ngan
1.
General
(a) write down all the relevant formulae
(b) beware of the units (SI units), all physical quantities have units
(c)
(d)
(e)
(f)
(g)
2.
3.
4.
5.
G = 109, M = 106, k = 103, m = 10-3,  = 10-6, n = 10-9
put reasonable values to the physical quantities in MCQ
copy the numerical values beside the objects in the figures
think with the extreme cases; use counter-proof to verify the answer(s)
don’t waste time on the questions involving complicated calculations
Optics
(a) concave mirror Vs convex lens (convergent); convex mirror Vs concave lens (divergent)
(b) convex mirror and concave lens have small, erect and virtual image only; bigger virtual
image must be formed by concave mirror or convex lens
(c)
(d)
(e)
five important places: beyond 2f, at 2f, between 2f and f, at f, inside f
three golden rules on ray construction
distant object means infinite object distance
(f)
use the formula
(g)
the only formula in refraction:
1 1 1
 
to check the answer(s)
f u v
1
n2 
sin 1
(nair = 1)
sin  2
Heat
(a)
(b)
(c)
the important formulae: E = mcT (no change of state), E = ml (change of state)
when using electrical heater, E = Pt; beware of the unit of time
temperature unchanged when state is changing
(d)
(e)
melting ice = 0C, boiling water = 100C
evaporation will happen at every temperature (above 0 K)
Gas Laws
PV
= constant; the unit of T must be in K
T
(a)
the powerful formula:
(b)
(c)
(d)
(e)
know the names of the three gas laws and their experimental details
know the graph in gas and beware of their coordinates
internal energy consists of kinetic energy (temperature) and potential energy (state)
higher temperature, higher KE; bigger separation, higher PE
Motions
(a)
(b)
when calculating the acceleration from a tape, be careful in counting the time (interval)
in free falling (vertical) motion, acceleration almost the same (= g) unless the object is
hitting on the ground
(c)
quantities in motion (u, v, s, t) are independent of mass of the object since there is no “m”
in the equations of motion
(d)
play much attention on the motion graphs, see what the axes are, including the square
terms.
in v-t graph:
(e)
slope = acceleration, +ve or –ve depends on the (tilting) direction of the line and not
on the region of the line
(ii)
area = displacement, over the time axis: +ve displacement, vice versa
both have units
(i)
6.
7.
Force and motion
(a) inertia can explain everything; mass always unchange
(b)
friction has its own limiting value, before this value, the value of friction is equal to the
applied force, but with opposite direction. beware of the friction when the motion is
changing from up the inclined plane to down the plane.
(c)
action and reaction pair: reaction force exists if and only if action force exited; action
and reaction forces act on two different bodies.
(d)
(e)
consider the weight of the object when the situation is in vertical; W = mg
try to feel your weight increased or decreased when you are in a lift while the lift is
ascending or descending
Force and Momentum
(a)
(b)
in a lever system, beware of the weight of the lever. moment can be taken at any points.
there are so many formulae in this chapter, but remember the golden one: F = ma, where
(c)
F is the net force
conservation of momentum: momentum almost conserve no matter what the perfectly
(d)
8.
Energy and Efficiency
(a) energy analogy
(b)
conservation of energy: loss in PE, gain in KE; verse versa
(c)
(d)
remember the work done against friction: WD = fs
beware with the inelastic collision, energy is not conserved (loss)
useful  output
(energy or power)
efficiency 
total  input
(e)
9.
elastic, elastic and inelastic collisions unless there exist an external force
golden rule: total momentum of a system before collision/explosion = total momentum
after collision/explosion
Waves
(a)
(b)
(c)
(d)
the only formula: v = f
all of the EM waves have the same velocity in vacuum, c = 3108 ms-1
definition of velocity: distance the wave traveled in unit time
velocity of the wave depends on the medium it travelling
(e)
(f)
frequency keeps unchanged everywhere unless the source (vibration) changed
wavelength changes with both frequency and velocity
(g)
the four wave properties: reflection (boundary/barrier), refraction (medium), diffraction
(gap/obstacle) and interference (two sources)
interference is the only property the wave has
path difference is very useful in finding wavelength
remember the EM spectrum; higher frequency implies lower wavelength, higher energy
it carries
know the difference between travelling wave and stationary wave.
know the words: in phase, out of phase, instantaneously at rest
(h)
(i)
(j)
(k)
(l)
10. Electrostatics
(a)
(b)
earth is an very large pool of charges with unlimited supply
charges will stay with the attraction of the rubbed rod no matter where the earth is
touching
11. Electric Circuit
(a) the golden formula: V = IR, remember V is the potential difference
(b) no current, no potential drop even there exist an resistor
(c) know how to find the potential at each point
(d) circuit connection: current in…+ve, current out…-ve
(e) ammeter has very small internal resistance while voltmeter has very large
(f)
(g)
(h)
(i)
when finding the equivalent resistance with complicated circuit, redraw the circuit
parallel circuit: same p.d.; series circuit: same I
current in branches is independent (from the others)
beware of the power consumption when domestic electrical appliances connected, the
rated value may not be true, but the intrinsic element (internal resistance) of the
appliance will be unchanged
12. Magnetic and Electromagnetic effects
(a) Fleming’s rules: current precede uses left-hand rule; no current uses right-hand rule
(b) remember the Lenz’s law
(c)
(d)
(e)
in an ideal (no loss) transformer, primary power = secondary power or Pp   = Ps
voltage depends on the turn ratio; secondary current depends on the electrical appliance
when calculating the value of shunt and multipler, think with same voltage in shunt and
same current in multipler
13. CRO and Electronics
(a) Y-input measures the voltage (potential difference) across the device; time base measures
the period of the a.c.
(b) CRO has infinite internal resistance when it is acting as a voltmeter
(c)
unleaded input carries high potential in logic gate
14. Radioactivity
(a)
(b)
(c)
 is a massive particle (large inertia)
remember the nature, penetrating power and ionization ability of the three particles
high ionizing power accompanies with low penetrating power
(d)
(e)
(f)
 carries positive current,  carries negative
Z = atomic number, A = mass number, don’t mix up
use simple method to count the undecay (remain) substance after certain period; count
number half-life