Electricity Flashcards
Electric charge can be
Positive or negative
An atom has the same number of electrons as protons
it is uncharged
What is a conductor and eg
Electrons flow through metals easily
Silver, gold, copper, steel
What is a insulator and eg
poor conductors of electricity
Eg: rubber, glass, plastic
Conduction in metals
Electrons are free to move around atoms
Under normal circumstances movement is random and there is no flow of charge
If a cell or battery is connected, the electrons move from the negative
What is current, unit, formula, and what do you measure it with
(Amperes)- rate or flow of charge
Current (A)= Charge (C) / Time (s)
Current is measured using an ammeter
Electric current flow
Flows from positive terminal to negative terminal
What is DC
Direct current (d.c)- Current flows in one direction (batteries)
What is AC
Alternating current (a.c)- Current constantly changes direction (mains supply)
What is Voltage, unit, formula, and what is used to measure it
(Volts)- also known as potential difference, electromotive force
The voltage across an electrical component is needed to make an electric current flow in it
Voltage (V) = Energy (J) / Charge (C)
Voltage is measured using a voltmeter
Characteristics of series circuit
- Same current throughout the circuit
- Voltage is shared between all the components
- Total resistance is the sum of the individual resistances of each component
Characteristics of a parallel circuit
- Voltage across each component is the same
- Total current is the sum of the currents through the separate components
- Every time another resistor is added in parallel, the total resistance decreases
Advantages of connecting 2 lamps in parallel instead of series
- Lamps can be controlled individually
- One lamp will continue working even if other does not
- Lamps are brighter than when connected in series
What is resistance, unit, formula
(Ohms)- opposition that an electrical device has to the flow of current
Moving electrons can collide with the ions in the metal and this causes resistance as it is more difficult for the current to flow
If resistance increases, current decreases
Resistance (Ω) = Voltage (V) / Current (A)
In a wire, what would increase the resistance
- Length of wire increases
- Thickness of wire decreases
Relationship between heat of a metal and resistance
The hotter the metal gets, the higher its resistance
* When a current passes through a metal the metal gets hotter and the ions vibrate more
* This causes more resistance as it is harder for the ions to get past the electrons
What is Ohm’s law
Current is proportional to the voltage
Current-voltage (I-V) graph for a resistor
Straight line through the origin
Obeys Ohm’s Law
Current-voltage (I-V) graph for a Filament lamp
Resistance of a filament lamp increases as the temperature
Lamp doesn’t obey Ohm’s law
Current-voltage (I-V) graph for a Diode
Current only flow through a diode in one direction
The diode has a very high resistance in the reverse direction
Thermistor
Resistance of a thermistor decreases as the temperature increases
Mains electricity
Electricity supplied to homes is called Mains Electricity
It is an alternating current supply
It has a frequency of 50 cycles per sec or 50 hertz
three pin plug and what each colour represents in the electric cable
- Live with brown insulation (carries current)
- Neutral wire with blue insulation
- Earth wire with yellow-green striped insulation
What is the earth wire
- Safety feature
- Connected to the metal casing of a device
- Other end of this wire is connected to a metal rod that goes to the ground
What are the dangers of main electricity
- Fire
- Electrocution
What is a fuse
Length of wire designed to melt and so breaking a circuit when the current passing through it goes above a certain level
The thicker the fuse the greater the current required to cause it to melt
What is a circuit breaker
Electromagnetic device that breaks a circuit when the current goes above a certain value
Comparison between circuit breaker and fuse
Fuses are simple and cheap to replace
Circuit breakers act more quickly than fuses and can be reset
What is double insulation
Casings made from an insulator such as plastic rather than metal
Appliances will only have two-wire cables as they do not need the Earth wire
Energy transferred
Energy transferred (J) = Voltage (V) * Current (A) * Time (s)
Electrical power equations
Power (W) = Energy (J) / Time (s)
Power (W) = Voltage (V) * Current (A)
What charge are protons and electrons
Protons are positively charged.
Electrons are negatively charged.
what does charging by friction do
When insulating materials rub against each other, they may become electrically charged.
Electrons, which are negatively charged, may be ‘rubbed off’ one material and on to the other.
The material that gains electrons becomes negatively charged. The material that loses electrons is left with a positive charge
What happens when a polyethene rod with a duster
Friction causes electrons to gain energy.
Electrons gain enough energy to leave the atom and ‘rub off’ onto the polythene rod.
the polythene rod has gained electrons, giving it a negative charge
the duster has lost electrons, giving it a positive charge
If the rod is swapped for a different material such as acetate, electrons are rubbed off the acetate and onto the duster.
the acetate rod has lost electrons, giving it a positive charge
the duster has gained electrons, giving it a negative charge
Both the rods and the duster are made of insulating materials. Insulators prevent the electrons from moving and the charge remains static.
Conductors, on the other hand, cannot hold the charge, as the electrons can move through them.
How can you check if an object is positively charged
When a charged object is held close to a conductor, electrons in the conductor are able to move towards (or away from) the charged object
The attraction between the positive rod and the negative charges on the top surface of the paper will cause the paper to be attracted to the rod.
Electrical forces
A charged object will experience non-contact force from another charged object.
The type of force will depend on the type of charge (positive or negative) on the two objects
The properties of attraction and repulsion are often used to show that an object is charged in 3 examples
*a charged rod can pick up small pieces of paper
*a charged balloon can stick to the wall by attraction
*a charged rod can pull a stream of water towards it
What is the law of charges
Like charges repel, unlike charges attract
Uses of static electricity
Electrostatic precipitators
photocopiers
Ink jet printer
Paint spraying
Problems with static electricity
*it is a nuisance when dust and dirt are attracted to insulators such as TV screens and computer monitors.
*it is a nuisance when clothes made from synthetic materials cling to each other and to the body, especially just after they’ve been in a tumble dryer
Dangers of static electricity
Static electricity can build up in clouds. This can cause a huge spark to form between the ground and the cloud. This causes lightning –a flow of charge through the atmosphere.
It is dangerous when there are flammable gases or a high concentration of oxygen. A spark could ignite the gases and cause an explosion.
It is 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. A person could die from an electric shock.
Refueling aircrafts and tankers also poses a particular danger. If the fuel passing along the hose to the vehicle was allowed to build up a static charge, a resulting spark might ignite the fuel. The hoses are earthed to stop this occurring.
What is a golden leaf electroscope
The gold leaf electroscope has a very very thin piece of gold foil (called gold leaf) fixed at the top to a piece of copper.
The copper has a large round top, called the cap. The whole thing is put inside a glass case, to stop air blowing the delicate gold leaf around. The piece of copper goes through insulationin the top of the glass case, so that any charge on the gold leaf cannot escape.
