Electricity Flashcards
Electric circuit
A continues and closed path of an electric current
Switch
Conducting link between a cell and the bulb
Hwo is electric current expressed
Amount of charge flowing through a particular area in unit time / rate of flow of electric charges
Direction of flow of charge
Direction of electric current is taken as opposite to the direction of the flow of electrons
electric current (
The flow of electric charge is known as Electric Current, Electric current is carried by moving electrons through a conductor.
electric potential difference (voltage)
The difference in the amount of electric potential energy between two points in an electric circuit is called electric potential difference.
Voltage formaula’s ( two main ones )
- V = IR
V = W/Q
ohm’s law
Ohm’s Law states that the potential difference between two points is directly proportional to the electric current, at a constant temperature.
resistance
obstruction offered by a conductor to teh flow of electric current
resistors in series
When the resistors are connected in series, the current flowing through each resistor is the same and is equal to the total current.R1, R2 and R3 = V1, V2 and V3
resistors in parallel
When resistors are joined in parallel, the reciprocal of the total resistance of the system is equal to the sum of reciprocal of the resistance of resistors.
work formula : ( one )
W = V × Q
power formula 2 (main ones) :
P = W/T
P = VIt
heat formula :
H = I^2Rt
filament of an electric bulb material
The filament of bulb is generally, made of tungsten metal, having melting point equal to 3380°C.
Quantization of cbarge
chareg transferred is always an intergral multiple of teh fundemental charge
conductivity
reciprocal of resistance
van der graaf (date of creation)
1929
Why does energy flow ? ( electricity move ??) (cbse)
The chemical reaction within the battery generates the potential difference between its two terminals that sets the electrons in motion
Why does electricity flow ? ( one line )
A battery Causes energy to flow in the circuit by introducing a difference in charge across it’s two terminals
Real current
Electrons carry negative charges so they are repelled or flow away from the negative terminal and are attracted to the positive terminal, this flow of electrons is called real current
conventional current
Conventional current always flows from high potential to low potential i.e from positive to negative ( opposite to the flow of electrons )
Covalent bonding
Sharing of one or more pairs of electrons ( shared electrons are bound into molecular energy orbitals of the atoms and cannot move form atom to atom )
Semiconductors
Are not like metals and don’t have a sea of delocalized electrons but can still conduct electricity ( but not very well ) averagely well and have some free electrons in their structure ( carbon has one ‘free’ lectern in graphite form )(usually covalent bonding)
Does air conduct electricity
Air is a mixture of neutral or inert gases. Therefore it contains few or no charged particles or free ions for conduction of electricity. Thsi makes it a poor conductor of electricity. However When the amount of the accumulated charges becomes very large and charge difference between the two points is great enough , air which is normally a poor conductor of electricity is not able to resist their flow. Thus, charges discharge through the air during lightning. Process is called electric discharge because electric current will flow as a discharge or spark.
When is a material said to be ohmic ?
When it exhibits a linear relationship between potential differance and current
Why do birds not get shocked but people on teh ground do
Birds have both feet on the wire so there is no conducting path for the electric current to flow to reach is lower potential so no current flows.
Why is heat generated
The heat is generated because electrons moving through the conductor collide with the atoms of the conducting material. When the electrons and atoms collide the atoms gain kinetic energy from the electrons and their thermal vibration increases.In other words the conductor begins to get hot as more atoms vibrate the more likely it is that electrons will collide and so the resistance of the conductor increases still further and even more heat is produced
What type of relationship is heat and electricity
Exponential
Resistance
The obstruction Offered by a conductor to the flow of electric current is called its resistance ( as collions suffered increases so does its resistance ). Depends on the arrangement of atoms and configuration of electrons in the conductor
Electrical conductivity
Reciprocal of resistIVITY. measure of ease with which a charge can flow in a conductor
Critical temperature
The temprature below which a conductor offers no electrical resistance is known as critical temperature. At critical temperature metal offers zero resistance to the passage of electricity
Electromotive force
Force between the terminals of the cell when np current flows
Terminal voltage
Potential difference between two terminals of teh cell when current is drawn from it
electric current
flow of energy carried by electrons
battery life is measured in ?
amp-hours
critical temprature
temperature at which te metal offers zero resistance to the passage of electricity
about teh third pin
the third pin is called teh earth wire. it runs into the ground at some point. intendeed to provide an alternative conductive path for any current taht has short circuited away from teh intended circuit.
what is power (2)
rate of doing work/rate at which energy is transformed.
what is efficiency
ratio of output power to input power
what is power? (2)
rate of doing work/rate at which energy is transformed.
What is the National Grid?
A system of cables and transformers linking power stations to consumers.
what is one amp
One amp is the current that flows when one coulomb of charge passes a point in a circuit in one second.
voltmeter vs ammameter placements
voltmeter - must be placed in parallel to teh component
ammameter - must be placed in series to teh componenet
National Grid
the entire system called that links powers stations and transmission lines to consumers
A step down transformer…
Lowers the current and increases the voltage
EMF abbreviation for ?
Electromotive force
EMF definition
The number of joules of energy given to each coulomb of charge that passes through the cell is the e.m.f. of the cell
Electromagnetic induction
The production of
an e.m.f. by moving a wire in a magnetic field is known as electromagnetic induction
The induced e.m.f. (and current) can be increased by:
Moving the wire faster
• Using a stronger magnet
• Increasing the length of wire in the magnetic field (eg. By looping the wire several times)
Faraday’s law of electromagnetic induction.
The e.m.f. induced in a conductor is proportional to the rate at which the magnetic field lines are cut by the conductor.
The induced e.m.f. (and current) can be increased by: ( in the case when a bar magnet is pushed into a coil of wire and therefore causes e.m.f. to be induced in the coil )
1) moving the magnet faster; (2) using a stronger magnet; (3) increasing the turns on the coil.
UK mains
230V, with a frequency of 50Hz (hertz).
Generator
In electricity generation, a generator is a device that converts mechanical (kinetic) energy into electrical energy for use in an external circuit.”
How is power transmitted though the cables and why !
Power is transmitted through the
Transformer
cables at high voltage so that the current is reduced and less heat is
produced. thinner, lighter and
cheaper cables can also be used.
Transformers
Transformers are used to increase or decrease voltages. Transformers will not work with DC.
Step up transformer
the voltage is increased between the primary and secondary coils.
Hwo do transformers work
When AC flows through the primary coil, it sets up an alternating magnetic field in the soft iron core and, therefore, in the secondary coil. This changing field induces an alternating voltage in the secondary coil.
The force on the wire is increased if:
The current is increased
• A stronger magnet is used
• The length of the wire in the
field is increased
Turing effect ( 3)
Inthecoilofwirethecurrentflows along one side in one direction, and in the opposite direction on the other.
2) According to Fleming’s left hand rule one side is pushed up by the magnetic field, and one is pushed down.
3) These opposing forces on the coil of wire will result in a turning effect.
The turning effect on the coil can be increased by:
Increasing the current;
• Using a stronger magnet;
• Increasing the number of turns on the coil;
• Increasing the area of the coil.
Field
A field is a physical quantity that has a value for each point in space and time.
Electromagnetic fuels in wires (3)
When a current flows in a wire (conductor), a magnetic field is produced.
• The polarity of the magnetic field depends on the direction of the current.
• Use the “Right Hand Thumb’s Up Grip Rule”
Solenoid
A solenoid is a long coil of wire.
Electromagnet
When a current flows through the coil it produces a magnetic field. This field is temporary and is lost when the current is switched off.
The core is usually made of a soft metal such as iron or Mumetal.
Relay
A relay is a device which uses a low current circuit to switch a high current circuit on or off.
