Chapter 11 Flashcards
How can an insulator be charged
By friction through the transfer of electrons
What happens to a material gaining electrons
It becomes negatively charged
What happens to a material losing electrons
It becomes positively charged
What do same charges do
repel
what do opposite charges do
attract
How can electrostatic shock occur
If you are electrically ‘charged’ and you touch something that is earthed or if you’re earthed (completes circuit) and you touch something that is charged the current passes through living material and causes an electric shock
In static electricity, what does it mean to be earthed
Connected to the ground directly or indirectly so the electric charge flows from an object, preventing a dangerous build- up of static electricity.
How does lightening occur
Static electricity building up in clouds which causes spark to form between ground and cloud. Lightening is caused by a flow of charge through the atmosphere.
How does attraction by induction occur, give example
A polythene rod is negativity charged prior by vigorously rubbing it with a cloth. Its the placed over pieces of paper. The paper sticks to the rod. This is because when the negatively charged polythene is brought close to the paper, the negative electrons in the paper are repelled downwards. The upper side of the paper becomes positively charged and therefore the 2 are attracted to each other.
How does earthing remove excess charge by movement of electrons
The excess charge is balanced by the transfer of electrons between the charged object and the ground.
What are some of the everyday uses of electrostatic charges in everyday situations
Photocopiers, defibrillators and paint sprayers.
Insecticide sprayers= They can be sprayed from aircraft so that they cover a large area. There is a risk that some of the spray will blow away or fall unevenly. To prevent this, the insecticide is given a static charge as it leaves the air craft. The static drops evenly as they all have the same charge and are attracted to the earth.
What is an electric field
A region where an electric charge experiences a force
What are some dangers of sparking in everyday situations
Static is dangerous when fueling cars as there are inflammable gases, vapours or a high concentration of oxygen. A spark could ignite the gases and cause an explosion.
Static can be dangerous when you touch something with a large electric charge on it. The charge will flow through your body causing an electric shock. This could cause burns or even stop your heart.
Describe the shape and direction of the electric field around a point charge
The pattern of lines is referred to as electric field lines. They point in the direction that a positive charge would cause if placed upon the line. Therefore if the lines are directed away from centre they are positive and if they are directed inwards they are negative
Describe shape and direction of the electric field between parallel plates
Placing 2 oppositely charged plates parallel to each other creates a uniform electric field. A charge would experience the same force of attraction or repulsion matter where it is located in the field= force is equal at all points in field
Describe shape and direction of the electric field relating to the concentration of lines.
The direction of the arrows shows the direction in which a positively charged particle will move. The spacing between the field lines gives an indication of the strength of the force. If the lines are close together then force will be greater.
How does the concept of an electric field help explain the phenomena of static electricity
x
What’s a permanent magnet
Magnetic all the time eg- fridge magnet
What’s an electromagnet
A magnet that can be switched on or off
How to increase the strength of a magnet
Increasing number of coils
Increasing current
What characteristics should a material for making an electromagnet have
Easily magnetised
Easily demagnetised
Eg- soft iron as its pure
Not steel as it would retain some magnetism when current is off
Why is a magnetic field produced when wire is wrapped around electromagnet
When a current is passed through a conductor a magnetic field is produced around it
Direction of field depends on direction of current
If current arrows are pointing down what direction is the field
Clockwise
If current arrows are pointing up what direction is the field
Anti-clockwise
In a coil where does the magnetic field go
Through centre of coil
What is a solenoid
A coil with lots of tight packed turns
What happens when you put a current carrying conductor in a magnetic field
A force would be exerted on it
What does the direction of force depend on
Direction of magnetic field
Direction of current
When do we use left hand rule and what do fingers stand for
Used when finding direction of force
First finger- magnetic field N to S
Second finger- Current
Thumb- motion or movement
Describe a practical to demonstrate left hand rule
Arrange 2 conductive metal rods with a lose rod straddled across them
If we put lose rod in a magnetic field & turn on current the rod will move
If we change direction of field or current the rod will move in the other direction
What is the electric motor effect
The fact a current carrying conductor in a magnetic field has a force exerted on it
How does an electric motor move
Consists of a coil in a magnetic field- the current flows in opposite direction on opposite sides of magnetic- opposing movements form a rotation
What’s the opposite effect to electric motor effect
A conductor passes through a field and produces current in the conductor
Direction of current depends on direction of field and direction of movement In conductor- when current is induced a generator is formed.
Flemings right hand rule-
Movement of conductor=thumb
Direction of field= first finger
Second finger= current
Describe 2 ways in a lab that we could investigate strengths of magnets
Bar magnets under a piece of paper and put iron filings on top to show force lines of magnet
Put compasses around a magnet to see how they line up north to south
What happens if a North and South Pole of 2 separate magnets are placed at short distances apart
The field lines go from North Pole of one magnet to South Pole of another- lines are parallel due to strong attraction
In VIR graphs what does a steep line show
Small resistance
In VIR graphs what does a shallow line show
Large resistance
Describe what the VIR graph would look like for a fixed resistor
Straight line
positive gradient, directly proportional
Follows ohms law
Describe what the VIR graph would look like for a filament lamp
We wouldn’t get a straight line because atoms are vibrating more= increasing chance of collisions with electrons and therefore increasing resistance
A curve dip and then curving to a peak- s shape
Describe what the VIR graph would look like for a diode
Straight line on top half and then moving up - increase in current only on positive side as diodes only allow current to flow in one direction.
Describe what the VIR graph would look like for a thermistor
Resistance decreases as temperature increases - peak to a trough- opposite to filament lamp line
What is ohms law (equation)
R= V\I
What is potential difference
Difference in energy carried by charge between 2 points in a circuit
What is ohms
Resistance
What does ohms law look like
Directly proportional- straight diagonal
