Knowt
physics
1. Physical Qty, Units and Measurement
• Precision of an instrument is the smallest unit that the instrument can measure.
• Precision of experimental results is a measure of how close the experimental results are to each other.
• Accuracy is a measure of how close the experimental result is to the true value or accepted value.
Base qty + units:
Mass (kg), Length (m), Temp (K), Current (A), Amt (mol), Time (s)
• A scalar is a physical quantity which has magnitude only. • A vectoris a physical quantity which has both magnitude and direction.
2. Kinematics
• Distance is the total length travelled by a body regardless of the direction of motion.
• Displacementis the distance measured in a straight line in a specified direction.
• Speedis the distance traveled per unit time.
• Velocity is the rate of change of displacement.
• Acceleration is the rate of change of velocity.
3. Dynamics
• Mass is the amount of matter in a body
• Weight Is the force of gravity acting on a body.
• A gravitational field is a region in which a mass experiences a force due to gravitational attraction
• Hooke’s Law states that within the limit of proportionality, the extension or compression, x,
• produced is directly proportional to the elastic force F. • Inertia refers to the resistance of a body to resist a change in the state of rest or motion of the body.
• Newton’s 1st Law of Motion states that a body will remain in its state of rest or uniform motion in a straight line unless acted upon by a resultant force.
• Newton’s 2nd Law of Motion states that the resultant force acting on an object of a constant mass is the product of the mass and acceleration of the object. The object accelerates in the direction of the resultant force.
• Newton’s 3rd Law of Motion states that if body A exerts a force on body B, then body B exerts an equal and opposite force on body A
4. Turning Effect of Forces
• The centre of gravity is the point through which the entire weight of a body appears to act for any orientation of the object
• The moment of a force is the product of the force and the perpendicular distance between the axis of rotation and the line of action of the force.
• The torque of a couple is the product of one of the forces and the perpendicular distance between their lines of action of the forces. • The Principle of Moments states that, for an object to be in rotational equilibrium, the sum of clockwise moments about any axis of rotation must equal the sum of anti-clockwise moments about that same axis.
• A body is in translational equilibrium when the resultant force on the body is zero.
• A body is in rotational equilibrium when the resultant moment on the body about every axis is zero.
5. Density and Pressure
• Density of a substance is defined as its mass per unit volume. • Pressure is defined as the amount of force acting perpendicularly on a unit area.
6. Energy, Work and Power
• Work done is the product of a force on a body and its displacement in the direction of the force.
• The principle of the conservation of energy states that energy cannot be created or destroyed, but can be converted from one form to another. The total energy of an isolated system remains constant.
• Poweris defined as the rate of work done or rate of energy conversion.
7. Light
• Refractive index of a medium is the ratio of speed of light in vacuum and in the medium.
• Focal length is the distance between the optical centre and the focal point.
• Critical angle is the angle of incidence in the optically denser medium for which the angle of refraction in the optically less dense medium is 90°.
• Total internal reflection is defined as the complete reflection of a light ray inside an optically denser medium at its boun dary with an optically less dense medium.
8. General Properties of Waves
• A wave is a propagation of a disturbance which carries energy from one point in space to another without transferring of matter. • Wave speed is the distance travelled by a wave per second • The amplitude of a wave is the magnitude of maximum displacement of the particle from its equilibrium position. • The frequency of a wave is the number of complete waves produced per second.
• The period of the wave is the time for a particle in the wave to complete one cycle of vibration
• The wavelength of a wave. is the shortest distance between 2 points which are vibrating in phase.
• The wavefront is an imaginary line or surface that joins points of a wave that are in phase.
• Transverse waves are waves in which the displacement of the particles of the medium is perpendicular to the direction of the direction of energy transfer.
• Longitudinal waves are waves in which the displacement of the particles of the medium is parallel to the direction of energy transfer. •Ultrasound is sound with frequencies above the upper hearing limit of the human range of audibility (audible: 20-20k, US: >20k Hz)
Definitions and Laws (IP4 2024)
9. EM waves
Components of EM spectrum
Properties of EM waves (10)
Examples of EM waves applications
Dangers of EM waves on living cells and tissue
10. Static electricity
Electrostatic charges consist of positive and negative charges, measured in Coulombs.
Law of electrostatics states that like charges repel and unlike charges attract
Electric field: region in which an electric charge experiences an electric force
Electrical conductors vs electrical insulators
Draw electric field lines of isolated point charge (direction of field lines = direction of F acting on positive test charge)
Describe the 2 ways of electrostatic charging: electrostatic charging by rubbing involving transfer of electrons and electrostatic charging by induction.
Rubbing: insulators
Induction: conductors
Describe experiments to show electrostatic charging by induction.
2 metal spheres vs 1 metal sphere
Discharging/neutralizing electrostatic charges from insulators and conductors
Describe eg of Electrostatic hazards
Lightning
Fires due to sparked cause from sudden electrostatic discharge
Damage to electronic equipment
applications of electrostatic charging
Spray paint
Photocopier
Electrostatic precipitator
11. CURRENT OF ELECTRICITY
Define current: rate of flow of charge (amperes)
Conventional current vs electron flow
Define EMF of a cell: Work done by source in driving unit charge around a complete circuit
Define PD across a component: Amt of electrical energy converted to other forms per unit charge passing through it
Formulas: (all electricity topics)
I=Q/t
V=RI
VJC: V=J/C (V: EMF/Voltage)
R=pL/A
E=Pt
When calculating cost of EE usage, express energy in lWh instead of J; since EE sold in kWh
P=IV, P=I2R, P=V2/R
E=QV
EMF vs PD
EMF: energy conversion within source (Chemical energy → Electrical energy)
PD: energy conversion outside source (Electrical energy → Heat energy/Light energy)
Effect of temperature increase on resistance of metallic conductor
Sketch and interpret I-V graph for:
metallic conductor at constant temperature (ohmic conductor)
Filament lamp
Semiconductor diode
12. DC CIRCUITS
Symbol for: DC supply, AC supply, fixed and variable resistors, variable potential divider, fuse, bell, Light-dependent resistor, thermistor, light-emitting diode
Current in series circuit vs parallel circuit: Current at every point in series circuit is same vs current across whole circuit = sum of current in separate branches in parallel circuit
PD in series vs parallel circuit: PD across whole circuit = sum of PD in series circuit vs PD across whole circuit = PD across separate branches of parallel circuit
Effective resistance for series vs parallel
Action of Negative Temperature Coefficient thermistors and Light Dependent Resistors
13. PRACTICAL ELECTRICITY
State the hazards of using electricity in the following situations:
Wires with damaged insulation
Overheating of cables
Damp conditions
State the meanings in terms of live neutral and earth
Safety features of household electrical circuits
Fuse, CB, switch: Connected to high voltage live wire so that when fuse blows/CB trips/switch opened during excessive current flow/elec fault, it cut off current to elec appliance AND appliance disconnected from high voltage of live wire → appliance not charged at high potential of __V → prevent electric shocks/safe to touch/repair
Current not necessary condition for voltage to be present (eg. when switch open on N wire, though no current flow in circuit, any pt betw live connection and switch remains charged at high potential
Fuse current rating slightly higher than max current req by elec appliance: if lower than that, fuse likely to blow and be changed frequently; if much higher, total current allowed b4 fuse melts much higher which risks overheating of appliance then there's excessive current
Three pin plugs (E, N, L) → must know how to identify!!!
Earth wire joins metal casing of appliance to ground
When have elec fault, earth wire diverts large current safely to ground thru alt pathway of lower resistance
→ excessive currentflow due to short circuit causes fuse to blow → break circuit+ disconnects appliance from high voltage of live wire (opt)
If no fuse, excessive current flow due to short circuit by earth wire overheats wire → fire
→ prevents one from getting an electrical shock from touching metal case
Double insulation: Outer casing + internal components insulated (w plastic)
14. MAGNETISM
Properties of magnets
Earth’s magnetic field
Magnetic vs non magnetic mat
Induced magnetism/temporary magnets through:
placing magnetic material near/in contact w magnet
Stroking continuously in one dxn
Place within current carrying solenoid
Temporary (iron) vs permanent magnet (steel) in terms of property and use
(not in LO) Define Magnetic field: region where magnetic material exp a magnetic F
Desc how a bar magnet (compass) can be sued to determine dxn of B-field
Properties of B-field lines
Draw B-field pattenr around 1) bar magnet 2) like and unlike poles of 2 bar magnets placed side by side and on top of each other
15. ELECTROMAGNETISM
X: into the pg * out of the page
currents in straight wires and solenoids
Draw the B-field for
state the effect on B-field of changing dxn of current
ways to increase B-field strength
Right Hand Grip Rule used to find 1) dxn of B-field ard wire 2) polarity of magnet
Describe application of magnetic effect of current in CB
Fleming’s Left Hand Rule applies to str wire or moving charge in uniform magnetic field
F on current carrying conductor in a magnetic field + the effect of reversing the current + reversing the dxn of the magnetic field
F on beam of charged particles in a magnetic field + the effect of reversing the current + reversing the dxn of the magnetic field
B-field of currents in parallel conductors
TEOF of current carrying coil: how to increase TEOF?
Action of DC motor
Action of split ring commutator
