Notes on the Alternative to Practical Paper
1. This paper is an alternative to a practical exam, not an alternative to a practical course.
2. The preparation for students is a well-designed practical course.
3. The course should teach candidates how to make measurements using many different types of instruments. They should see the instruments, handle them, discuss their scales and the scale units before using the instruments.
4. Students should understand why the choice of range for the measuring scale should match the size of the quantity being measured.
5. Students should know how to record measurements in a table. A table should record all the measurements needed to obtain the value of a given physical quantity. For example if a length l is derived from l = l2 - l1 then l1 and l2 should appear in the table. Columns (or rows) in the table should be headed with the name of symbol of the physical quantity. The unit in which the quantity is measured should be included. The SI method is recommended. Encourage neat work.
6. Ideally, when performing an experiment (and relevant readings are recorded) it is helpful to arrange the experiment so that one variable is increased step by step. Candidates should always look for a trend in the recorded results. Some trends are
· y increases as x increases
· straight line through the origin, if x is doubled then y is doubled, direct proportionality
· y decreases as x increases
· x times y = k, inversely proportionality. Inverse proportionality is generally not properly understood
7. A graph is the best way to display the results of an experiment.
· y/unit against x/unit should be understood as the label of each axis
· axes should
q be labelled with quantity, unit and scaled
q as large as possible, but should not use an awkward scale to achieve the size
· plotting should be neat and as accurate as possible
· graph lines should be neat, thin and a good fit (if there is scatter of points they should lie either side of the line{in a rough way!! }). Straight lines should FILL the page (even beyond the range of points) so that any gradient calculation can use the largest Dy and Dx. Students should understand why! (Dy is a measurement.)
· students should describe what information is obtained from a graph, see note 6.
8. Students should understand the idea of a fair test or comparison in which only one variable is altered at a time, eg when investigating how rate of cooling experiment depends on temperature room to be kept constant--room draughts, volume and type of liquid, amount of stirring.
9. Students should be trained to give a conclusion to an experiment.
10. Good procedures: -
· repeat readings to spot anomalous errors or to calculate an average
· avoid making parallax errors, {the line of sight should be perpendicular to the reading on the scale}
· look carefully at any scale that is used eg
q notice the unit in which the scale is calibrated - always give the unit of any measurement
q notice the maximum reading that can be obtained
q notice the smallest change in value that can be obtained
q aim to use quantities that have magnitudes that are towards the upper values of the scale
· in experiments involving the measurement of a length
q try to use lengths that are at least 100 mm in length
q you can measure to the nearest mm with a rule, or perhaps 0.5 mm
q when measuring heights ensure that the rule is held perpendicular to the base
q know how to arrange apparatus so that it is parallel or perpendicular to a bench
q know how to arrange a set square either side of a cylinder/sphere to measure diameter
· in light experiments using objects, lenses and a screen
q ensure that each item is aligned so that the centre of each item is at the same height and on the same horizontal straight line (ideally use the term optic axis)
q use a fiducial aid when measuring a length, eg mark the middle of the lens on the bench
q try to use a translucent screen
q perform the experiment in a shaded part of the laboratory
· in ray tracing experiments
q when using marker pins space the pins so that they are at least 60 mm apart
q ensure that the pins are vertical
q draw neat thin lines
q use the largest angles available and draw the arms of the angle longer than the radius of any protractor being used, ie a large radius is desirable
· when using a thermometer
q position the eye so that the mercury thread appears to touch the scale
q decide whether you can read between the marks on the thermometer, ie some thermometers can be read to better than 1 ºC even though the marks are every º C
q check whether the thermometer is full or 1/3 immersion
· in heat experiments
q choose volume/mass values of the quantities that give large changes in the temperature
q insulate the container, cover the container
q stir and wait for highest temperature after stopping heating
· in electrical experiments
q check for a zero error
q tap the meter to avoid sticking
q initially choose the highest range for the ammeter/voltmeter, then reduce the range for the ammeter so that the deflection is almost full scale
q always check polarities before closing the switch (completing the circuit)
q always check that connections are clean.
q switch off the current when not making a measurement.
q when measuring resistance use low currents/voltages to avoid heating and changing the resistance you are measuring
· when measuring an interval of time
q a stopwatch can measure to about 0.1 s, although it may give a reading to 0.01 s
q for oscillations (of a pendulum or vibrating rule), be able to define a complete oscillation
q time N oscillations, usually N>10 and use the terminology periodic time T = t/N
q explain how to use a fiducial aid at the centre of the oscillation
q explain where the eye should be placed to avoid parallax errors
Current Electricity
Current electricity is the flow of electrons (flow of charge)
| | electrons are moving steadily in definite direction - continuously through some conductor |
| | electrons flow from point of excess electrons to point of deficiency of electrons |
| | separation of charge produces electromotive force (EMF) |
| | EMF pushes electrons through conductor |
In an electrical circuit, current is the means by which energy is transferred from a source such as a battery or generator to a load (lamp, motor, or other device that absorbs electrical energy and converts it into some other form of energy or into work).
EMF - potential difference that exist across a battery, generator, etc. when it is not connected to any external circuit. The potential difference across the terminals of a source is always less than EMF due to internal resistance.
Complete electrical circuit:
4 parts:
| | source of electrons - dry cell |
| | conducting path for electrons - wire |
| | device to open and close circuit - switch |
| | purpose of circuit - load |
Other sources of electrons include electrochemical cells and electrical generators.
Electric plug - electrons leave negative terminal at source, go through switches into house, through one side of plug, through appliance or load, then out through other prong and back to positive terminal of source
Loads (resistances) - powered by moving electrons which must move through load before they can return to source
Switches - control circuit
Fuses - interrupt flow of current if flow becomes too great for wires to hold it safely (or appliance to use it safely). Fuses contain a small piece of wire that melts if too much current passes through it. Most household fuses will blow at 15 - 20 amps.
Circuit breakers - shut off current if too much flows (open switch)
Semi-conductors - silicon and germanium - conduct electricity poorly - resistance decreases with increasing temperature
Super-conductors - behave like normal materials at normal temperatures - at extremely low temperatures resistance decreases and vanishes = no energy loss when current flows
See electrical symbols here
Ohm's Law: Current = Voltage
Resistance
Resistance
I (amps) = V (volts)
R (ohms)
R (ohms)
Current:
Direction, by convention, is the direction in which positive charges would move. A current is always assumed to move from positive terminal of a battery or generator to negative terminal in circuit.
Direction, by convention, is the direction in which positive charges would move. A current is always assumed to move from positive terminal of a battery or generator to negative terminal in circuit.
Actual electrical currents in metal consist of flow of electrons.
A current of negative particles moving in one direction is electrically the same as a current that consist of positive particles moving in the opposite direction.
Symbol = I unit = ampere (amp) measured by ammeter
Definition = rate of flow of electrons past a certain point
Example = gallons of water coming out of a pipe per second
Definition = rate of flow of electrons past a certain point
Example = gallons of water coming out of a pipe per second
1 amp = the flow of 1 coulomb of electrons passing one point in one second
1 amp = coulomb = 6.25 E 18 electrons
second second
second second
1 electron = charge of -1.6 E - 19 coulomb
a current of 1 amp in a metal wire has 1 coulomb's worth of electrons (6.25 E 18) passing a point every second.
The following chart list sample amperage ratings for common tools:
| bug killer 1-2 | fan = 1-3 | hedge trimmer 2-3 | weed trimmer 2-4 |
| electric drill 3-6 | saber saw 4-8 | sander 4-8 | band saw 5-12 |
| lawn mower 6-12 | grinder 7-10 | chain saw 7-12 | drill press 7-14 |
| belt sander 7-15 | router 8-13 | shop vac 8-14 | lawn edger 9-10 |
| air compressor 9-15 | table saw 12-15 | snow blower 12-15 | circular saw 12-15 |
| 1/4 HP motor = 6 amps | 1/2 HP motor = 10 amps | 3/4 HP motor = 14 amps | 1 HP motor = 16 amps |
Voltage
Symbol = V unit = volt measured by voltmeter
Definition = the driving force behind electrons; the work done per unit charge to move that charge from point A to B; the work required to get electrons passing some point per second
volt = joule = unit of work (F x d)
coulomb # of e-/second
coulomb # of e-/second
If battery has a rating of 1 volt it is capable of doing 1 joule of work for each coulomb of charge that it delivers
Resistance
Symbol = R unit = ohm (Ω) measured by ohmmeter
Definition = opposition to flow of electrons; the ratio between potential difference (V) and the resulting current flow (I)
ohm = volt
ampere
ampere
A conductor in which there is a current of 1 amp when a potential difference of 1 volt exist across it has a resistance of 1 ohm.
Resistivity
Resistances of conductors that obey Ohm's Law depend on:
| | material of which it is composed - the ability of a material to carry an electrical current varies more than almost any other physical property |
| | length - the longer the conductor the greater the resistance |
| | cross-sectional area - the thicker the conductor, the less its resistance |
Resistivities of nearly all substances vary with temperature. In general: metals increase in resistivity with increase in temperature and nonmetals decrease in resistivity. ΔR = α R Δt
Electric Power
Electric power = current x potential difference
Unit of power = watt (amp x volt)
Unit of power = watt (amp x volt)
The power consumed in causing a current to flow is dissipated as heat.
P = IV (power = current x voltage)
P = I2 R (power = current squared x resistance)
P = V2
R (power = voltage squared divided by resistance)
R (power = voltage squared divided by resistance)
brightness = I V
Sample Problems:
1. A light bulb has a resistance ob 240 ohms. Find the current flowing in the circuit when placed in a 120 volt circuit.
(I = V/R 120 volt/240 ohms = 0.50 amp)
(I = V/R 120 volt/240 ohms = 0.50 amp)
2. The current in the coil of a 8 ohm loudspeaker is 0.5 amp. Find the voltage across its terminals.
(V = IR 0.5 amp x 8 ohm = 4 volt)
(V = IR 0.5 amp x 8 ohm = 4 volt)
3. Find the resistance in a circuit that has a voltage of 120 volts and a current of 4 amps.
(R = V/I 120 volts/4 amps = 30 ohm)
(R = V/I 120 volts/4 amps = 30 ohm)
4. In a simple house circuit there is an amperage of 0.6 amps and a resistance of 20 ohms. What is the voltage in this circuit?
(V = IR 0.6 amps x 20 ohms = 12 volts)
(V = IR 0.6 amps x 20 ohms = 12 volts)
5. If a 100 watt light bulb burns for 10 hours, how many watt-hours of electricity are used?
(watt = volts x amps watt-hour = watt x hours
1000 watt-hours = 1 kilowatthour)
(watt = volts x amps watt-hour = watt x hours
1000 watt-hours = 1 kilowatthour)
Series Circuits
In a series circuit electrons flow along a single path through 2 or more loads before returning to source.
Law #1 - any break in a series circuit stops the entire electron flow (a break or loose connection can prevent electrons from flowing)
Law #2 - when there are two or more loads in a series circuit, the voltage drop across each load is a fraction of the total voltage supplied by the source
| | voltage across each load decreases as additional loads are wired into circuit |
| | the sum of the voltage drops across each load = voltage of source |
| | V1 = I R1 V2 = I R2 V3 = I R3 |
| | VT = V1 + V2 + V3 + ... |
Law #3 - the current is the same in all parts of a series circuit - all electrons flowing from source eventually return to source - only one path in series circuit - can measure current anywhere in circuit
Law #4 - the resistance (total) increases in a series circuit as the number of loads increases - the total resistance of a circuit is equal to the sum of the resistances of each wire and load
RT = R1 + R2 + R3 + ...
RT = R1 + R2 + R3 + ...
Parallel Circuits
A parallel circuit is one in which electrons flow through more than one path or branch. The electrons can flow through any one or more of the branches before returning to the source.
Law #1 - a break in one branch of a parallel circuit does not stop the flow of current in other branches
Law #2 - the voltage is the same in all branches of a parallel circuit and equals the voltage of the source
Law #3 - the current is not necessarily the same in all branches of a parallel circuit. The sum of the current drops in all resistances equals the total current flowing through circuit.
| | I1 = V/R1 I2 = V/R2 I3 = V/R3 |
| | IT = I1 + I2 + I3 + ... |
Law #4 - The total resistance in a parallel circuit decreases as the number of loads or individual resistances increases. The total resistance is less than that of the smallest single resistance. All branches act as one broad pathway which offers less resistance to the flow of electrons than any single pathway.
1/RT = 1/R1 + 1/R2 + 1/R3 + ... or
RT = ( R1 x R2) / (R1 + R2)
ELECTROMAGNETIC SPECTRUM: THE MEMBERS, IN DECREASING and DECREASING ORDER OF WAVELENGTH AND FREQUENCY RESPECTIVELY IS CODED HERE AS R I V U X - G
R = RADIO WAVES
I= INFRA-RED
V = VISIBLE RAYS (MEMBERS are CODED INTO R O Y G B I V , ALSO IN THE SAME ORDER AS IN ABOVE. R stands for red light, O for Orange, etc.)
U = ULTRA-VIOLET
X = X-RAYS
G= GAMMA RAYS
NOTE: MICROWAVES ARE SHOT WAVELENGTH RADIO WAVES. A separate band may be created for it between radio waves and infrared, but since they are radio waves, such separate band is not necessary.
| | waves | sources | detector | uses |
| 1 | Radio waves | Radio and TV transmitting antenna, galaxies and stars | Radio aerial | · Communications through radio and TV · Telephone links · Microwaves for cooking food |
| 2 | Infrared | Hot objects, electric fire, the sun | · Special films · Skin. · Blackened thermometer · Electronic detectors | · Infrared remote control · Heating · Taking temperature picture ( in infrared camera) · In heat therapy for treatment of muscular pains |
| 3 | Visible light | The sun, very hot objects | · The eye · Photographic film · electronic detectors | · seeing · photography · photosynthesis · information transmission |
| 4 | Ultraviolet | The Sun, Mercury vapour lamps, electric arcs in welding operation | · Photographic film · Electronic detector | · Used in fluorescent lamps · Sterilizing food · Security marking · Used in photosynthesis by flora · To examine eggs in poultry; old eggs glow purple while fresh glow scarlet. |
| 5 | X -rays | X- ray tube | Photographic film | · In medical diagnosis( CAT scan) · Medical treatment e.g of cancer · In engineering to know the structure of crystal |
| 6 | Gamma rays | Radioactive materials e.g uranium and cobalt | Photographic film, electronic detector, Geiger- Muller tube | · Radiography · Treatment of cancer · Measuring thickness in enginnering |
| | | | | |
Kinematics
Definitions
Distance: The total length travelled by a moving object irrespective of direction. Its SI unit is meter (m).
Displacement: The distance travelled in a specific direction. Its SI unit is meter (m).
Speed: It is the rate of change of distance or distance travelled per unit time. Its SI unit is meters per second (m/s).
Velocity: It is the rate of change of displacement. It is speed in a specific direction. Its SI unit is meters per second (m/s).
Acceleration: It is the rate of change in velocity. Its SI unit is meters per second per second (m/s2).
Formulae
Distance: Speed x Time, [In case of constant acceleration]: {(Final Speed + Initial Speed)/2} x Total Time Taken.
Displacement: Velocity x Time, [In case of constant acceleration: {(Final Velocity + Initial Velocity)/2} x Total Time Taken.
Speed: Distance Travelled/Time Taken.
Average Speed (in case of constant acceleration): (Final Sped + Initial Speed)/2.
Velocity: Displacement/Time Taken.
Acceleration: Final Velocity – Initial Velocity/Time Taken.
Acceleration of Free Fall
It is the acceleration due to gravity.
It is given the symbol g.
The acceleration due to gravity is 10m/s2.
The direction of this acceleration is towards the centre of the Earth.
This acceleration does not depend on the masses or weights of objects.
During free fall motion there is an opposing force to the motion known as air resistance.
When an object falls in a uniform gravitational field, it accelerates until air resistance is equal to the pull of gravity. It then continues at a constant velocity which is known as terminal velocity.
Distance-Time Graph
The gradient of distance time graph gives us speed.
Speed-Time Graph
The gradient of speed-time graph gives us acceleration.
Physics Formula Revision (Conditions highlighted in red) [Draft Ver]
| Topic | Formula | SI unit | Final unit |
| 2.1: Kinematics |  | Distance (m) Time (sec) | m/s |
 ; | Displacement (m) Time (sec) | m/s | |
 Condition: Used only when acceleration is constant. | Velocity (m/s) Time (sec) | m/s2 | |
| 2.2 Dynamics |   | Force (N) Mass (kg) Acceleration (m/s2) | Newton (N) |
| 2.3 Mass Weight Density |  | Mass (kg) g = 10 N/kg | Newton (N) |
 ;. | Mass (g/kg) Volume (cm3/m3) | g/cm3 or kg/m3 | |
| 2.4 Turning Effect of Forces |  | Force (N) Perpendicular Distance (m) | Newton metre (Nm) |
| Note: Perpendicular Distance is not always the length of the rod. | |||
| 2.5 Pressure | Solids:  | Force (N) Area (m2) | N/m2 , Pa |
| Liquids:  | h (m): Depth of Liquid  (kg/m3): Density of liquidg: 10N/kg | N/m2 , Pa | |
| Gases (when temp. is constant)  | P (Pa): Pressure V (m3): Volume | NA | |
| 2.6 Energy, Work, power |  | F (N): Force d (Perpendicular dist): m | J |
 | m (kg): Mass v (m/s): Velocity | J | |
 | m (kg): Mass g: 10N/kg h (m): Height | J | |
| X  | Energy change /Work done(J) Time (s) | J/s, W (watt) | |
| 3.1 Principles of Thermometry |  (For Celsius scale only) | Theta: Unknown temperature X0: “ice point”, X100: Steam pt | oC |
| 3.2 Thermal Properties of Matter |  | C: Heat capacity | J |
 | m: mass c: Specific Heat Capacity | J | |
 |  : Latent heat of fusion | J | |
 |  : Latent heat of vapourisation | J | |
| 4.1: General Wave Properties |  | f: Frequency t (sec): Time | Hz |
 | v (m/s): Velocity  (m): Wavelengthf(1/t): Frequency | m/s | |
| 4.2: Light | Snell’s Law:  | n = refractive index (ratio) i/r (o): angle of incidence/refraction *Set calculator in degree mode. | NA. Ratio. |
| Condition: The angle of incidence must be in the less dense medium; angle r must be in the denser medium. | |||
| 4.2: Light |  | c (m/s): Speed of light in vaccum (3x108 m/s) v (m/s): Speed of light in medium. | NA. Ratio. |
| |  | c (o): Critical angle. | o |
| 5.1: Current Electricity |  | I: Current (A) Q: Charge (Columb) t: Time (sec) | Coloumb, C |
| |  | W: Work done/energy of circuit (J) Q: Charge (Columb) | V, J/C |
| |  | V: Potential Diff. (V) W: Work done/energy across circuit component Q: Amount of charge | V, J/C |
| | Ohm’s Law:  Condition: Only for ohmic conductors. | R: Resistance (  ) | V |
| |  | : Resistivity (m) L: Length A: Cross-sectional Area | |
| 5.2: Practical Electricity |  | | J |
| |  | P = Power R = Resistance | W |
| 5.3: Electromagnetic Induction |  | | |
