PHY- electricity

effects of current:

• lighting and heating
• magnetic: deflects a compass
• chemical

unit of current: AMPERE(A)

current is measured using an ammeter

unit of charge: coulomb(C)

conventional direction of current: positive to negative

electron flow: negative to positive

series:

• current remains same
• voltage changes
• V= V1+V2 => IR= IR1+IR2=> ( Since current is same), V= V1+V2

parallel

• current divides, gives preference to path with less resistance
• voltage remains same all across
• Ieq= I1+I2 => (V/Req) = (V/R1) +(V/R2) => (1/Req) = (1/R1) +(1/R2)

FACTORS AFFECTING RESISTANCE

• length: longer the wire, more the resistance
• diameter: greater the diagmeter or cross sectional area, lower the resistance
• R= p*(l/A)       [ Stands for rho]

PD

• the difference in electrical potential between two points on a circuit; pd is required to push the current through the resistor and make ut flow
• measured in volts by a voltmeter
• the potential difference across a battery or cell is called the EMF(electromoive force)
• emf cannot be considered a force as the formula f=ma doesnt apply in this situation.

• the opposition of a conductor to conduct is its resistance
• V= IR
• unit of resistance is 'ohm'

RESISTORS:

• conductors intended to have a resistance are called resistors.
• variable resistors are used in electronics.
• if current in a metallic conductor is proportional to its resistance the it is an OHMIC RESISTOR
• Semiconductor diode: conducts in one directio only and is a non-ohmic resistor; lets current flow only in one idrection
• Filament lamps:non ohmic resistor when temperatures are high; 
• High temperatures usually inc. resistance of conductors however it does the opposite for semiconductors.
• Thermistor: as temp inc. resistance dec.
• Light dependent resistors: resistance dec. as light intensity inc.
• Transducers:  an input transdu=cer is a device whose elctrical properties change with respect to environmental changes

Relays:

• type of switch that works using an electromagnet
• there will be 2 circuits when a relay is used.
• the electromagnet coil of relay is in one circuit; represent with a rectangle
• the switch is on the second circuit; normal representation
• current flows through first circuit with the relay coil and it becomes magnetised
• it pulls the second switch which closes the second circuit and allows current to flow

Diodes:

• component that only allows electric current to flow in one direction
• some diodes give out light when current passes through them.They are called light emitting diode.
• useful from converting AC to DC. the diose acts as a rectifier.

Potential Divider

• is a circuit that uses resistors to supply a variable potential difference.

ELECTRIC POWER

E=VIT ; P=IV ; P= V "2/R.

Fuse:

• protects a circuit
• stops excessive current from flowing
• a fuse contains a thin section of wire designed to melt away if the current gets above a certain value. its melting breaks the circuit.

Fused plug:

• electricity comes to our house via an underground cable consisting of a live and neutral wire.
• the live wire supplies AC with alternating positive and negative current
• live- brown
• neutral- blue 
• earth- yellow and green; this wire is connected with the metal case of an electrical appliance.

ELECTRICAL SAFETY

• Earthing
• Circuit breakers: 
  • consists of an electromagnet
  • when current exceeds its range, the electro magnet gains enough strength to full apart a point of contact and break the circuit.
  • operate faster than a fuse and can be reset by pressing a button.

• circuit breakers[...]
  • there are 2 types of circuit breakers- (a) a trip switch and (b) a residual-current device.
  • trip switch:  when current is too high, the device 'trips' hence breaking the flow.
  • RCD:  works by detecting differences in the circuits of live and neutral wires. it breaks the circuit before any damage is caused. user friendly. 
• Double insulation: 
  • connection to the supply is through a two core insulated cable with no earth wire. the appliance itself is enclosed in a plastic casing.

input sensor => processor => output transducers

• transducer: a device used to convert non-electrical signals into electrical ones and vica versa
• input sensor: detects changes in environment and convert their energy to electrical.
• processor: decides the action bsed on the electrical signal recieved.
• output transducer: converts electrical signal to another form. ex:lamp

input transducers:

• Light dependent resistance: resistance dec. as light increases
• thermistor: resistance dec. as temperature increaes

output transducers:

• relays: electromagnetic switch'
• light-emitting diode: when forward-biases, light is emitted. when reverse-biased, none emitted.

there are two main kinds of electric circuits- digital and analogue.

ANalogue:

• voltages can have any value over a certain range
• variable resistor is analogue. in a circuit with a lamp, it allows the lamp's light to vary over a wide range.
• analogue meters show their reading by the deflection of a needle over a continuous scale

Digital:

• voltages only have one of 2 values. either high or low.
• switch is a digital device
• digital readers display their readings as digits.

• logic gates are switching circuits which are used in computers and electronic systems.
• the device recieves one or more input signals. on the basis of those it produces an apt output signal.
• high voltage is considered ON and represented with a vertical line-  |
• low voltage is considerd OFF and represented with a circle- o

AND gate

• both input one and 2 have to be ON for the output to be ON

OR Gate

• either input one/2 has to be ON for output to be ON

NOT Gate

• the input has to be OFF for the output to be ON

a truth table shows all the possible combinations of inputs and their corresponding outputs on the basis of the type of logic gate.

NAND Gate

• output is OFF when both the outputs are ON

NOR Gate

• output is ON when neither input one nor two are ON

• V=IR
• Q=IT
• P=IV
• E=VIT
• R(eq)= R1+R2+R3 [SERIES]
• V(eq)= V1+V2+V3 [SERIES]
• I(eq)= I1+I2+I3  [SERIES]
• (1/R)= (1/R1)+(1/R2)+(1/R3)