Physics (Paper 2) 🔥 Flashcards
(SP8/9)
Energy definition
the ability to do work or cause a change
Work done definition
Energy transferred
Equation for work done
Force x Distance
Work done is measured in
Joules
Time is measured in
Seconds
Energy stores/transfers
• GPE
• EPE
• Chemical
• Kinetic
• Nuclear
• Electrostatic
• Magnetic
• Thermal
• Sound
How is force worked out?
Mass x acceleration
Contact force definition
A force that acts between two touching objects
Reaction force definition
The force of an object at rest on a surface
Air resistance definition
the force of an object moving through the air
Upthrust definition
Upward force exerted by liquids
Non contact force definition
A force acting between 2 objects that do not touch
Examples of contact forces
Upthrust, friction, reaction force
Examples of non contact forces
Gravity, magnetism and electrostatic force
Scalar tells us the…
Magnitude (size) of a force
Vector tells us the…
magnitude and direction of a force
What is Newton’s Third Law of Motion?
For every action there is an equal and opposite reaction
Equilibrium definition
When forces are balanced or cancel out
Friction definition
Force between 2 surfaces sliding
Resultant force
Overall force acting on an object
(aka net force)
Net force definition
Sum of the forces applied on object (overall force)
Moment definition
Turning force
Moment equation
Force x Distance perpendicular to force
Clockwise moment is equal to…
anti clockwise moment
A free body diagram models the
Forces acting on an object
Examples of vectors
• Velocity
• Displacement
• (any force eg friction, weight, normal force)
Moment is calculated in
Newton metres
Equation for Weight
Mass x gravitational field strength (10 N/kg)
Examples of scalar quantities
• Temperature
• Energy
• Speed
• Time
(SP10)
Electrical circuit definition
a closed path where electrons flow in a wire
Series circuit
Only has one pathway or loop
Parallel circuit definition
A circuit in which current can flow through on multiple paths
Diode definition
A component that only allows current to flow in one direction
What is the unit of charge (Q)?
Coulomb (C)
What is the unit of current?
Amperes
What does LDR stand for?
Light Dependent Resistor
What does LDR (Light Dependent Resistor) mean?
Resistor that depends on light intensity. As the light intensity decreases the resistance increases and vice versa
The direction of current flow is from..
the positive terminal to the negative terminal of the power supply
Current meaning
Rate of the flow of charge
Charge =
Current x time
Energy transferred equations
voltage (V) x Charge (Q)
or
Voltage (V) x Current (I) x Time (t)
or
Power (P) x Time (t)
Voltage meaning
Energy transferred per unit charge
(V = E/Q)
What type of circuit are ammeters connected in?
Series
What component can only be connected in a parallel circuit?
Voltmeter
Voltage equations
V = Current (I) x Resistance (R)
V = Energy transferred (E) / Charge (Q)
V = Power (P) / Current (I)
Current is directly proportional to
Voltage
Unit for resistance
Ohms
Resistance meaning
Opposition to current
As resistance increases, what happens to current?
Current decreases
How to work out the total resistance in a series circuit?
Adding up all the individual resistances (Rtotal = R1 + R2 + Rn)
How to work out the total resistance in parallel circuits?
Reciprocal of each of the resistances added together
(1/Rtotal = 1/R1 + 1/R2 + 1/Rn)
Thermistor
Resistor that responds to temperature
Ohms law
Current flowing through a conductor is directly proportional to the voltage (V = IR)
Power definition
The rate at which energy is transferred per second
Unit for power
Watts
Equations for power
P = I (Current) x V (Voltage)
P = I² (Current²) x R (Resistance)
P = E (Energy transferred) / T (Time)
(SP8) Kinetic energy equation
KE = 0.5 x mass x velocity²
Mass is measured in
Kg
Weight (and all other forces) is measured in
Newtons
How does resistance affect current in filament lamps?
As the current increases the temperature also increases • Increase in temperature increases the resistance • Causes current to increase at slower rate • (I-V graph has S shaped curve through origin)
What’s the relationship between voltage and current in diodes?
The current through a diode flows in one direction only • The diode has a very high resistance in the reverse direction so current is unable to flow • (I-V graph slopes upward with nothing shown on bottom side of graph)
Relationship between current and voltage in fixed resistors
• Current is directly proportional to voltage • Temperature remains constant • Resistance remains constant • (I-V graph presented as a straight line through origin as it obeys Ohm’s law)
AC meaning
Alternating current • Current that changes its direction back and forth
DC meaning
• Direct Current
• Current that flows in the same direction (positive terminal to negative terminal)
Characteristics of the UK domestic supply
- Supply is AC
- Frequency is 50 Hz
- Voltage is 230 V
What power supplies produce direct current?
Cells and batteries
Difference between AC voltage and DC voltage
In DC the voltage remains constant whereas in AC the voltage changes between positive and negative
When resistors are connected in series the resistance (Increases/decreases) and why ?
Increases
because the sum of resistances of individual resistors is equal to the total resistance
When resistors are connected in parallel the resistance (increases/decreases) and why?
Decreases
because the current has more pathways to go through therefore it’s easier for current to flow
Frequency meaning
Number of cycles (number of times the current changes direction) each second
Why do wires become hotter when an electric current passes through them?
• As electrons flow through wires, they collide with the positive ions in the wire which causes the ions to vibrate more
• This increased vibration of the ions increases the temperature and resistance of the wire
• Energy has been transferred from kinetic energy into thermal energy
Live wire
Copper wire coated with brown plastic • Carries alternating current at 230V
Neutral wire
Copper wire coated with blue plastic • Completes the circuit and is at 0V
Earth wire
Copper wire coated in green and yellow striped plastic • Used for safety and is at 0V
Function of fuse
Prevents electrical circuits from excessive current • Melts if current gets too high
What happens once the fuse melts?
The circuit is broken and no more current can flow through the device
As I-V graphs curve what happens to resistance?
It increases
How would you reduce unwanted energy transfer through wires?
By using thicker wires with a lower resistance to minimise heat produced
Advantages and disadvantages of the heating effect of an electric current
Advantages:
Provides warmth for electric heaters and kettles
Disadvantages:
- Often a form of wasteful energy
- Can lead to overheating and potentially a fire
How do LDRs increase in resistance?
When light intensity decreases
What happens to the resistance of a thermistor as temperature increases?
It decreases
What happens to the resistance of a filament lamp as temperature increases?
It increases
Application of LDRs or Thermistors
Used in sensor circuits: eg thermostats which regulates the temperature in heating/cooling systems
(SP8) GPE equation
• GPE = mass (kg) x gravitational field strength (N/kg) x vertical height raised (m)
• mgh
Unlike charges (attract/repel)
Attract
Like charges (attract/repel)
Repel
The more friction that occurs within a circuit…
The higher the resistance and the less electrons that flow
How does an insulator become charged by friction?
When two insulating materials are rubbed together, electrons are transferred creating an imbalance of charge that’s built up
Why do insulators not lose its charge?
Electrons can’t be conducted in an insulator
Earthing
The removal of excess charge by the movement of electrons
What happens during a spark?
The electrons jump between 2 charged objects creating a visible discharge of electricity
Static electricity meaning
The build up of charge on insulators
Objects normally have a neutral charge overall. Explain why.
Normally, the number of positive protons is equal to the number of negative electrons, so the charges balance each other making the overall charge neutral.
How does lightning occur?
• In a storm, clouds move over each other and causes them to become charged as electrons are transferred
• The build up of negative charge in the clouds jump as it attracts to the positive charges on the ground
• It creates a giant spark as the potential difference is large enough to overcome the resistance of the air
Why can sparks be dangerous?
They can cause a fire by igniting flammable gases and liquids eg petrol
Meaning of force
A push or pull acting on an object
How does current compare in series and parallel circuits
Current is the same throughout a series circuit but splits in parallel
How does voltage compare in series and parallel circuits?
Voltage is split across components in series but is the same throughout parallel circuits
Electrical field
A region where an electric charge experiences a force
Where are electrical fields weakest on a charged object
At the edges
What direction do field lines go in positive and negative objects?
Positive : Outwards
Negative : Inwards
How many watts is a MW?
1,000,000 W
Charging by induction
When the magnetic field of a charged object induces a charge on a neutral object
The closer together the arrows are in field lines…
The stronger the electric field
Examples of items that become charged by friction
Polythene rod, cloth and balloons
What subatomic particle is transferred to make an object charged?
Electrons, -e
Why do materials that gain electrons become negatively charged?
Electrons are negatively charged particles and the imbalance of electrons creates an overall negative charge
How do we experience shocks from everyday objects?
When we touch a charged object the excess charge flow through our bodies creating an electric shock
How does earthing remove excess charge?
When objects are connected to the ground (through conductors) any excess charge will flow into the ground and neutralise the charge
How do insecticide sprayers use static electricity?
• Insecticide is given a charge as it leaves the sprayer • The droplets then repel each other as they have the same charge • This helps it cover a large surface area
Dangers of refuelling a vehicle
Flammable fuel runs through pipes at a fast rate • The friction between the fuel and the pipe causes the fuel to gain charge • Build up of charge may cause a spark and ignite the fuel creating an explosion
How is sparking prevented during the refuelling of aeroplanes ?
A bonding line carries excess charge from the plane to the Earth to neutralise the charge • This is a form of earthing
How do you calculate efficiency?
Useful energy transferred / Total energy supplied
Devise a method a student could use to investigate how resistance changes with potential difference
[Ensure a lamp, voltmeter, variable resistor and ammeter is included in circuit]
• Measure the current using ammeter
• Measure potential difference with voltmeter
• Vary the potential difference
• Calculate the resistance
• Repeat experiment and compare results
How do you find resistance on an IV graph?
Draw a tangent to the curve
[Topic 12]
What metals do magnets attract?
• Iron
• Cobalt
• Nickel
• Steel
In what direction do magnetic field lines flow?
From North to South
Where is the magnetic field strongest?
At the poles
What is a permanent magnet?
A magnet that produces its own magnetic field
What is an induced magnet?
A material that becomes a magnet when placed in a magnetic field
Electromagnet meaning
A solenoid with an iron core
How would you use plotting compasses to determine magnetic field lines?
• Place compass on paper near magnetic field
• Draw arrow in direction the compass points
• Repeat at different points on paper
• Join the arrows to make complete field line
What does a magnetic compass contain?
A small bar magnet pointing in direction of Earth’s magnetic field
What’s a uniform magnetic field?
• One that has the same strength and direction at all points
• Equally spaced apart
Evidence for the Earth’s core being magentic
In the absence of magnets/magnetic materials, a magnetic compass would always point north as it attracts to core’s magnetic field
What happens when current flows through a conducting wire?
A magnetic field is produced
What is the shape of a magnetic field produced by a current?
• Concentric circles
• Circles get further apart as field weakens further out
What represents current going IN and in what direction does the magnetic field
go?
• An X
• Field lines going a clockwise direction
What represents current going OUT and in what direction does the magnetic field
gо?
• A dot
• Field lines go in an anti clockwise direction
How can we increase the strength of an electromagnet?
• Increase number of turns in coil
• Increase current
• Add an iron core
When does the motor effect occur?
When a wire with current flowing though is placed in a magnetic field and experiences a force
How does an electric motor work?
• The power supply applies a potential difference across the coil
• A current flows through the coil
• A magnetic field is created around the coil
• The magnetic feld interacts with the magnetic fleid of the permanent magnets
• This creates a force that makes the coll spin
Why do the opposing sides of a coil in a dc motor feel a force in opposite directions?
Current is flowing in opposite directions on each side
What does a split ring commutator do?
• Reverses the direction of the current every half turn
• Keeps coil rotating continuously
Factors affecting the speed at which the coil rotates
• Size of current
• Magnetic field strength
How can we change the direction of rotation of the coil?
• Reverse direction of current
• Reverse direction of magnetic field (poles of magnet)
How can we increase the force supplied by the motor?
• Increase the size of current
• Increase magnetic field strength
• Add more turns to coil
Why does the coil rotate continuously in a dc motor when there’s current?
• The split ring commutator causes the current to reverse direction
• This reverses the direction forces are acting and so coil continues to rotate
Equation for magnetic force on current carrying conductor
F = BIL
Force (N) = Magnetic field strength (T) x Current (A) x Length of conductor in field (m)
How can we use Fleming’s left hand rule to determine force? (FBI)
• All 3 fingers must be held perpendicular to each other
• Thumb represents force direction
• 1st finger represents magnetic field direction
• 2nd finger represents current direction
