electricity Flashcards
which particle in an atom can freely move around
delocalised electrons
what is static electricity
buildup of charge in 1 location caused by 2 insulators
like charges __ unlike charges ___
repel,attract
when are electrons transfered
when objects become charged
what happens when 2 insulators are charged by friction
one ends up negatively charged due to having elections being lost and the other becomes negatively charged because excess electrons were transfered
what happens when a negatively charged insulator touches another insulators
the negatively charged insulator attracts the protons in the normal insulator when the charged insulator discharges its electrons to the normal insulator
how does lightning happen
in storms 2 clouds rub against eachother which causes friction between the water vapours,then one of the clouds becomes charged and is attracted to the positive ground which causes it to discharge
whats the unit and definition for current
- rate of flow charge
measured in amperes (A)
what does I=Q/T mean
current in A is equal to charge in columbs divided by time in seconds
whats the unit and definition for voltage
-energy transfered per columb of charge (basically the force applied to move electrons)
-volts
whats the unit and definition for resistance
-anything that opposes the electric current
-ohms (Ω)
whats the difference between cells and batteries
a cell is a single unit which converts chemical to electical energy
battery is a collection of cells
whats the symbol of a fuse what is its function
its like a resistor with a line drawn through the middle , its designed to melt and break when the current exceeds its limit
what is meant by LED and LDR
-LED (play button and arrows go outwards in symbol) is light emitting diode, it emits light while allowing current to flow in only 1 direction
-LDR (resistor with arrows pointing inwards) is light dependent resistor
which way are ammeters connected and what do the measure
connect in series and measure current
which way are voltmeters connected and what do the measure
connect in parallel and measure voltage
whats the relationship between voltage,energy transfered and charge
V=E/Q
what happens in parallel circuits
current is divided and the voltage stays the same
what happens in series circuits
voltage is divided and current stays the same
whats happens when resistance increases
voltage and current will also increase to overcome it
what is ohms law
current is proportional to voltage at constant temperature and resistance
what happens if temperature increases
resistance increases due to particles vibrating more frequently with more kinetic energy
what are the iv characteristics of a fixed resistor
-ohomic conductor
-straight line and linear graph
if y=current and x=voltage then
the steepest line is the highest resistance
if y=voltage and x=current then
the shallowest line is the highest resistance
how do fillament lamps work
the wires heat up then electric energy is transferred to infrared rays that emit light
whatre the iv characteristics of a filament lamp
-nonohomic conductor
-as current increases theres more of an heating effect so the wire heats up more causing increases resistance due to electrons coliding more often
-line plateus due to max voltage
what are the iv characteristics of a diode
at negative end theres super high resistance and at the start of positive end the voltage and current are trying to overcome resistance then finally the resistance decreases
what are the different variables for the required practical
controlled; resistor (filament lamp/diode/fixed resistor)
dependant(measured): current
independent(changes): voltage
whats the procedure for the required Practical
- connect any resistor filament lamp or diode to a series circuit that looks like this (draw diagram with variable power supply,ammeter,volmeter connected with lamp in parallel)
-keep resistance constant and change voltage using variable power supply
-flip batteries to measure both polarities
-plot iv graph and calculate resistance
-(for each component explain the characteristics theyll get when they plot it)
when does resistance increase in a thermistor
when its cold due to it being a negative temp coefficient so it acts opposite to normal resistor .
in thermistor, as temp increases, resistance ___
decreases
in LDRs as light increases,resistance __
decreases
what happens in ldr when its dark
very high resistance so more current is neederd to overcome it
how do LDR sensors work when its dark
the resistance is very high so more voltage and current is needed to overcome it. since lamp is connected in parallel to ldr the voltage is shared so the voltage increases in both ldr and lamp and more light is emitted
what happens to LDR sensors when its light
the resistance decreases so less voltage is needed to overcome it. since in lamp is connected in parallel to ldr voltage is shared, not much voltage is transfered through both the lamp and ldr so little light is emitted
why will a decrease in light intensity of LDR decrease ammeter readings
because resistance will increase as theyre inversely proportional
can static electricity happen between a insulator and conductor?
no because they wont transfer energy to eachother
why will resistance of metal filament increase as voltage increases
since the filament is metal it contains free electrons so when current flows through so does voltage and the temp increases which causes atoms to virbrate faster and colide more frequently
voltage= current X _____
resistance
describe how a student would use __ circuit to determine resistance in resistor r
switch on the battery and close the switch then record initial values of both ammeter and voltmeter. adjust the variable resistor to change the current then take the new reading. plot an iv graph and find the gradient R=V/I
what is the unit of power
watts (W)
