Physics Paper 1

• Forces

  • applied forces
  • weight
  • friction
  • normal reaction force
  • electrostatic forces
  • magnetic forces
  • upthrust
  • air resistance (drag)
  • tension
• Newton's 1st Law

  when the resultant force acting on a body is 0, the object doesn't accelerate. It remains stationary or continues to move in a straight line at a constant speed
• Explain how an object reaches terminal velocity.

  At first, the only force acting is weight, downwards.

  Air resistance is equal to 0, so forces are unbalanced, and the resultant force is downwards, so the object accelerates downwards.

  As speed increases, so does air resistance.

  This decreases the downwards resultant force.

  The object still accelerates downwards but at a decreasing rate.

  Eventually, air resistance becomes big enough to balance the object's weight.

  Forces become balanced, so ΣF=0.

  Object's speed becomes constant - reachest terminal velocity.
• Explain terminal velocity once a parachute opens.

  When the parachute opens, air resistance suddenly increases, while weight remains constant.

  Resultant force is pointing upwards so the object decelerates.

  As object decelerates, air resistance decreases until it balances weight again.

  Object reaches a lower terminal velocity.
• Hooke's Law:

  extension of a spring is proportional to the force applied
• Elastic behaviour:

  material returns to its original shape/length when stretching force is removed
• Hooke's Law Experiment

  Measure length of a spring with a ruler, with no masses attached, from eye level, to avoid parallax error.

  Add masses one by one, measuring extension with a ruler by eye level after each added mass.

  Draw a graph of force against extension.

  If line is straight and passes through the origin and is directly proportional, the spring obeys Hooke's Law.
• Elastic Limit:

  Up to this point, material shows elastic behaviour. Beyond this, material changes shape permanently and doesn't obey Hooke's Law.
• What increases thinking distance?

  • tiredness
  • alcohol and drug influence
  • distractions
  • increased speed, therefore slower reaction time
• What can increase braking distance?

  • increased speed
  • road conditions, icy + wet
  • car conditions, bald tyres/heavy load/poor brakes
• How does a fuse work?

  It contains a thin wire.

  If there's a surge in current, the wire melts.

  Therefore causing a gap in the circuit, and breaking it.

  Current no longer flows.
• What are the advantages of a circuit breaker over a fuse?

  It is resettable and works instantly.

  It doesn't require an earth wire and is more sensitive.
• How does a circuit breaker work?

  If there's an imbalance of currents between the live and neutral wire;

  An electromagnetic switch opens, making the circuit incomplete.
• How does an earth wire work?

  Earth wire is connected to the metal casing of an appliance.

  If live wire touches the metal casing, the appliance goes live.

  The earth wire provides a low-resistance path to earth.

  There is a surge of current in the earth wire;

  So the fuse melts, and the circuit breaks.
• Insulation:

  plastic used to cover the outer part of a plug.

  Double Insulation:

  all metal parts of the appliance covered in an insulator, like plastic.

  Current can't flow through the insulator if the appliance goes live.

  User doesn't get electric-shocked.

  An earth wire is not needed.
• How does current cause a heating effect?

  Wires have resistance;

  Electrons transfer energy as they flow through the wire;

  Due to electron collision with the lattice ions in the coil, a heating effect is produced.
• Hazards associated with electricity use:

  Using water (good conductor) together with electricity.

  Frayed cables.

  Overloaded sockets; overheat, lead to fires.

  Misusing equipment; sticking metal objects into sockets.
• Series Circuit:

  Current: is the same everywhere in the circuit, depends on applied voltage and other components.

  Voltage: shared between components; the more bulbs added, the dimmer they'll be.

  Resistance: total resistance is the sum of all the individual resistances.

  Advantages: less wiring, single switch to control all bulbs.

  Disadvantages: gap in circuit if one bulbs breaks; all bulbs stop working. No independent control.
• Parallel Circuit:

  Current: divided between branches.

  Voltage: each branch receives same voltage, even if more bulbs are added, they remain bright.

  Resistance: total resistance is smaller than least resistance in the circuit.

  Advantages: independent control. Switches can be placed in different parts of the circuit to control individual bulbs. If one bulbs breaks, only those on the same branch are affected.

  Disadvantages: more wiring.
• Ohm's Law:

  Current is directly proportional to voltage, given that temperatures remain constant.
• How temperature affects resistance:

  At higher temperatures, lattice ions in the wire vibrate more vigorously;

  So there are more frequent collisions with free electrons;

  Resistance increases;

  Rate of flow of charge decreases.
• Experiment to investigate how current varies with voltage for different components:

  Set up the circuit.

  Turn the variable resistor to its maximum value

  Close the switch and take voltmeter and ammeter readings.

  Alter variable resistor values and take new readings.

  Repeat this process at least 6 times.

  Place results in a table and plot a graph of current against voltage.
• How resistance varies in a metal filament lamp:

  Voltage and current follow a linear relationship for low values.

  Resistance during these low values is constant (constant gradient on a graph).

  Due to temperature increases for higher current and voltage, the graph becomes non-linear.

  Because of temperature increase, the lattice ions in the wire vibrate with more amplitude.

  So there are more frequent collisions between electrons and lattice ions.

  Resistance increases, and the rate of flow of charge decreases.
• Diode:

  Diodes allow current to flow through one direction easily due to low resistance in the given direction.

  In the opposite direction, there's high resistance so it allows very little current through.
• Waves:

  Waves are a means of transferring energy from one place to another without matter being transferred; particles vibrate about fixed position.
• Transverse waves: particles vibrate perpendicular to the direction of wave propagation; EM waves, sea waves.

  Longitudinal waves: particles vibrate parallel to the direction of wave propagation; sound waves.
• Amplitude = maximum displacement of a particle from its equilibrium position

  Wavefront = line connecting points which are in phase and the same distance from the source

  Frequency = number of complete oscillations in one second

  Wavelength = distance between a particular point on a wave, and the same point on the next wave

  Time period = time taken for a complete wave cycle
• Doppler Effect

  The change in frequency or wavelength of a wave signal, caused by the relative movement between the wave source and the observer.
• Stationary wave source:

  The observer receives the same frequency and wavelength from the source whether in front or behind it.
• Wave source moving towards an observer:

  Observer receives a higher frequency and shorter wavelength than the wave produced at the source.

  Wavefronts get compressed;

  Wavelength decreases so frequency increases;

  Wavelength and frequency are inversely proportional given that wavespeed remains constant.
• Wave source moving away from an observer:

  Observer receives a lower frequency and longer wavelength than the wave produced at the source.

  Wavefronts get spread out;

  Wavelength increases so frequency decreases;

  Wavelength and frequency are inversely proportional given that wavespeed remains constant.
• Electromagnetic waves:

  • all transverse
  • travel at the speed of light in a vacuum
  • transfer energy
  • can be refracted/reflected/diffracted
• Radiowaves:

  Uses: broadcasting TV and radio signals

  Hazards: minimal hazard, carries little energy and passes through body
• Microwaves:

  Uses: cooking food, communications using satellite transmissions, mobile phone signals

  Hazards: heating of body tissue (close oven door), perceived risk of cancer (monitor exposure and use a hands-free cellphone)
• Infrared:

  Uses: remote controls, toasters, ovens, heaters, IR cameras for looking at heat loss from buildings, night vision cameras

  Hazards: risk of skin burning and cell damage (avoid hot places, avoid Sun exposure, wear reflective clothing)
• Visible light:

  Uses: seeing + lighting, laser light: fibre optic cables, reading CDs, DVDs, barcodes, eye surgery, welding back a detached retina

  Hazards: eye damage (wear sunglasses and avoid Sun exposure)
• Ultraviolet:

  Uses: killing bacteria in water purification, hand driers in toilets, sterilization of equipment, medical uses in setting dental fillings, treatment of skin diseases like psoriasis, security markers for checking banknotes, fluorescent lamp for tanning beds, detecting blood and other bodily fluids

  Hazards: risk of cell damage; skin cancer and cell mutation (use sunscreen), eye damage; cataracts and blindness (wear sunglasses, avoid exposure)
• X-rays:

  Uses: taking shadow pictures of bones in bodies, security luggage checks, detecting cracks in buildings

  Hazards: risk of cancer and cell damage (limit/avoid exposure, use lead shielding, monitor exposure)
• Gamma rays:

  Uses: detecting cancer using a PET scanner or gamma camera, treating cancer using radiotherapy or focused gamma rays, sterilizing hospital equipment and food (kills bacteria)

  Hazards: risk of cancer and cell damage (avoid/limit exposure, use lead shielding or film badge, monitor exposure)
• Luminous objects: light emitted enters our eyes

  Non-luminous objects: light they reflect enters our eyes