Flashcards in Topic 2 Electricity Deck (45):
The flow of electrical charge
What happens to the current in a single closed loop
The current is the same everywhere in the circuit
What pushes the charge around the circuit
What is resistance
Anything that slows the flow down
What does larger resistance mean for current
Current is smaller
What does total charge depend on
Current and time
Resistance in ohmic conductors
They have a constant resistance. The resistance doesn't change with current. At a constant temperature The current flowing through it is directly proportional to the Pd.
The resistance of filament bulbs change. When electrical charge goes through it some energy is transferred to thermal energy store. Resistance increases with temperature so as the current increases so does the heat and resistance
The resistance depends on the direction of the current. It allows current to flow in one direction but have a high resistant if it is reversed
LDR (light dependent resistors)
Is a resister that is dependent on intensity of light. In bright light the resistance falls. In darkness the resistance is highest. Applications are automatic night lights, outdoor lighting and burglar detectors
Is resister dependent on temperature. In hot conditions the resistance drops. In cool conditions the resistance goes up. They make good temperature detectors e.g. Car engines, temperature sensors and electronic thermostats
LDRs and Thermistors in sensing circuits
Sensing circuits are used to turn on or increase power to components depending on the conditions
What is a series circuit?
Is when complements are connected in a line from end to end. If a component is disconnected or broken the circuit is broken.
Potential difference in serious circuits
It is shared by components so the Pd around the circuit add up to the sieve Pd
Current in series circuits
The current is the same as all components
Resistance in a series circuits
The resistance adds up so more components makes a higher resistance
Cell potential difference in series circuits
Potential differences are added together if they are connected to same way so two 1.5V cells are in the same circuit the Pd supplied will be 3V
What are parallel circuits?
In parallel circuits the components are separately connected to the supply. Removing a component hardly affects the circuit. Things usually made from this
Potential difference in parallel circuits
The same across the components. All components get the source Pd
Current in parallel circuits
Current is shared between branches all the currents of the components equals the total current. The total current going into a junction must be equal to ten current leaving. If two identical components are connected in parallel then they have the same current
Adding a resistor in a parallel circuit
Reduces the total resistance.
AC (alternating current)
Mains supply is AC. AC's current is constantly changing by alternating into from positive to negative and back. AC supply in your home is about 230V average and 325V peak. The frequency of mains is 50Hz
DC (direct current)
Batteries supply DC. DC is always flowing in the same direction and it's created by direct voltage
Blue wire completes the circuit and carries away current. Electricity flows in through the live wire and out through the neutral wire and is 0 V. Left wire
Brown provides Alternating potential difference at an average of 230 V. Right wire
Green and Yellow for safety stops the casing from becoming live doesn't have a current unless there is a fault 0 V. middle wire
They have a core of copper and a coloured plastic the colour represents it's use
Live wires giving electric shocks
Your body is 0V so touching a live wire will cause 230V to pass through you and the current can injure or kill you. Can still happen even if it isn't on as long as there a connection between the live and earth it is a danger
The national grid
A giant system of transformers and cables to connect power stations to consumers.
They have to meet demand for the time of the day. They predict when the most electricity will be used when people get up and get back from work or school. Power stations run below their maximum capacity in case of shut downs of other stations. Lots of smaller power stations are ready to be started up quickly.
Pd and current in the national grid
It used a high Pd and low current. High current or Pd is needed for high power. Current is not viable as it losses lots of thermal energy through the wires. It is cheap to boost the Pd up to 400,000 V and keep current low.
The step up transformers increase the Pd to 400,000V. The step down transformer brings the Pd down for safe usable levels.
Kettles transferring energy
Energy is transferred electrically from AC to thermal energy heating the inside of the kettle
Fan transferring energy
Transferred electrically from battery to kinetic energy stores in the fan's motor
Efficiency of electric appliances
The higher the current the more energy is transferred to the thermal energy stores so is more efficient
Energy transferred per charge passed
Build-up of static
Friction causes a a build-up of static. When certain insulating materials are rubbed together negatively charged electrons will be scraped off one and dumped on another. Leaving one negatively charged and the other positively charged. Example polythene negative and acetate positive when rubbed with a cloth duster
Movement of electrons
Only electrons move to form the positive or negative object
To much static
Too much static causes sparks. An electric charge builds up and the Pd increases and eventually the electrons can jump across the gap and cause sparks. It can also jump to any earthed conductor e.g. Getting an electric shock from a car.
Repelling and attraction
Like charges repel and opposites charges attract. The forces weaken as the distance increases. These forces cause the objects to move if the forces are strong enough this is known as electrostatics attraction or repulsion
Created around an electrically charged object. The. Loser the object the stronger the force.
Drawing electric fields
Electric field lines go from positive to negative. At a right angle to the surface. The closer the lines the stronger the field strength
Charged objects In an electric field
When a charged object is in an electric field it feels a force of attraction or repulsion. The force is caused by the electric fields interacting with each other. Increasing the distance decreases the strength of the forces between them
Drawing two oppositely charged particle
The two electric fields interact. Causes the forces to act on the two particles. These forces move the two particles closer together