Physics Flashcards
How does an insulator become charged?
Electrons are transferred from one material to another by friction
What is charging caused by?
A loss or gain of electrons
What is important to remember about like charges?
They will repel
What is important to remember about unlike charges?
They attract
What happens when an appliance short circuits?
The live wire of an appliance touches the neutral wire
What is an earth wire used for?
If there is a fault in the circuit, the earth wire carries the charge into the ground
Circuit symbol for a cell
A longer vertical line parallel to a shorter parallel line on the right
Circuit symbol for a battery
Multiple cells joined together
Circuit symbol for lamp
Circle with a cross inside
Circuit symbol for a resistor
A clear rectangle
Circuit symbol for variable resistor
A rectangle with a diagonal arrow pointing from bottom left to top right
Circuit symbol for ammeter
Circle with an A inside
Circuit symbol for voltmeter
Circle with a V inside
Circuit symbol for switch
Two circles connected by a straight line
Circuit symbol for diode
A circle with a triangle and straight line inside
What is the difference between direct and alternating current?
An alternating current repeatedly reverses direction
What is the difference between conductors and insulators?
A conductor allows energy to pass through it whereas an insulator doesn’t
Examples of conductors
Copper and aluminium
Examples of insulators
Plastics and rubber
Equation for current
Charge flow / time
What are voltmeters used for?
Measures the potential difference across a component
Equation for resistance
Potential difference / current
What does the V-I graph for a fixed resistor look like?
A diagonal line from bottom left to top right directly through the origin
What does the V-I graph for a filament lamp look like?
A curve from bottom left to top right passing directly through the origin
Properties of LDRs
Resistance decreases with light intensity
Properties of ideal diodes
Allows the current to flow in one direction only
What are the rules for current in a series circuit?
The same current passes through each component
What are the rules for voltage in a series circuit?
The total potential difference is shared between the components
How to calculate the total resistance in a series circuit?
Add the resistances of each component
What are the rules for current in a parallel circuit?
The total current is the sum of the currents passing through the branches
What are the rule for potential difference in a parallel circuit?
The potential difference across each component is equal
Why is the total resistance in a parallel circuit less than that of any individual resistor?
The potential difference remains the same. Adding a resistor increases the current entering the system
Resistance = p.d./i so resistance decreases
Equation for voltage
Energy transferred / charge flow
What are the two equations for power?
Current x voltage
Current^2 x resistance
What does energy transferred equal?
Power x time
What is the north pole of a magnet?
The end of the magnet that will always point north
What is the south pole of the magnet?
The end of the magnet that will always point south
What is attraction?
The force between two unlike poles
What is repulsion?
The force between two like poles
Describe the magnetic field around a magnet
Lines point in a direction away from the north pole towards the south, the magnetic field is more concentrated at the poles
What is the difference between soft and hard magnets?
Hard magnetic retain their magnetism and are difficult to demagnetize, soft magnetic materials are easy to demagnetize
Describe induced magnetism
An unmagnetized material can be magnetized by placing it inside a magnetic field
What is the difference between permanent and electromagnetism?
A permanent magnet retains its magnetism over a long period of time, whereas electromagnets can be magnetised and demagnetised
How to increase the magnetic field of a solenoid
Increase the strength of the current
Can reverse its direction by reversing the direction of the current
Characteristics of solids
Particles are tightly packed
Characteristics of liquids
Particles are packed together but less tightly than solids. Liquids take on the shape of their container
Characteristics of gases
Particles are held together loosely
What is the effect of temperature on particles?
The particles move faster with more kinetic energy and collide more frequently
What is the effect of pressure on particles?
The particles are held closer together so collide more often
At constant temperature, what will both pressure and volume be?
Constant
What is melting point?
The temperature at which a solid melts
What is boiling point?
The temperature at which a liquid turns into a gas
What is the latent heat of fusion?
The amount of heat energy required to change 1g of a substance from the solid to liquid state without changing its temperature
What is latent heat of vaporisation?
The amount of energy required to change 1g of a substance from the liquid to gaseous state without changing its temperature
Equation for density
Mass / volume
What happens to density as you move from solid to gas?
It decreases
How do you determine density experimentally?
The amount of water displaced when an object is placed in a body of water is its volume. Use this and its mass to calculate density
Equation for pressure
Force / area
Equation for hydrostatic pressure
h x p x g
h = Height of column
p = density of liquid
g = acceleration of gravity
Equation for hydrostatic pressure
h x p x g
h = Height of column
p = density of liquid
g = acceleration of gravity
What are thermal conductors?
Materials that allow heat to travel through them
What are thermal insulators?
Materials that don’t allow heat to travel through them
Examples of thermal conductors
Steel, copper, aluminium
Examples of thermal insulators
Plastic, wool, foam
What factors affect the rate of conduction?
Temperature difference across the material
Thickness of material
Thermal conductivity of material
What impact does temperature have on the density of fluid?
Increasing temperature = increased volume = decreased density
What will happen to a wire carrying a current in a magnetic field?
It will experience a force
How to remember the factors affecting the direction of a force on a wire?
The left hand rule - first finger = field
- thumb = movement
- second finger = current
What are the factors affecting the direction of a force on a wire in a magnetic field?
Magnetic field and current
What are the factors affecting the magnitude of a force on a wire in a magnetic field?
Size of current, strength of magnet
How do you calculate the force on a wire?
Force = magnetic flux density x current x length
How is a dc motor constructed?
A coil rotates inside a magnetic field
An electric current is induced
The output comes via split ring output
As the coil turns, the split-ring commutator reconnects The coil the opposite way around each the circuit each half turn
This means that the wire will only be connected to one half of the output
Therefore, the current flows in one direction only
What are electromagnets used in
Cranes, motors, doorbells
When will a voltage be induced in a wire?
When a wire cuts a magnetic field
How does an ac generator work?
The movement of the bar magnet induces a p.d. in the coil
This p.d. creates a current because the coil is part of a complete circuit
When will the outcome of the generator be highest?
When the plane of the coil is parallel to the magnetic field
Use a magnet with a strong magnetic field
More turns on the coil of wire