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level: Practical Electrical and Electronic Circuits

Questions and Answers List

level questions: Practical Electrical and Electronic Circuits

QuestionAnswer
what is done to prevent LED's becoming easily damaged by large currentsthey are placed in a voltage divider circuit with a fixed resistor known as a protective resistor
what is a transistor?voltage controlled electronic switch
where can you find transistors?a single component as part of a circuit or part of integrated circuits on a microchip
what do NPN transistors consist ofthree parts of two types of semi conductor material. N type and P type
name one type of semiconductor materialsilicon
what must happen in order for current to flow through the NPN transistor - in detailwhere n and p type material join, a potential difference is created. this must be overcome for current to flow through
what are the three parts of an npn transistorbase collector emitter
how is an npn transistor set upwith an input device connected to the base and the collector connected to the positive supply, emitter connected to the negative supply
how can an npn tranistor be switched onthe voltage at the base must be above 0.7V, this is enough to overcome the potential difference and allow electrons to flow from the emitter to the collector
what does MOSFET stand formetal oxide semiconductor field effect transistor
what are the different parts of a MOSFETgate, source, drain
how can you switch on a MOSFETa positive input voltage greater than 2V applied to the gate.
describe in detail how a MOSFET is switched ona 2V input voltage applied to the gate creates an electric field between the gate and the back electrode. The electrons in the p type material are attracted to the positive gate. It makes a channel of electrons allowing current to flow through the transisotr from the source to the gate.
how can you tell a circuit is seriesthe components are connected one after the other in the circuit
describe current in a series circuitcurrent in a series circuit is the same at every point It = I1 = I2 = I3 it doesn't matter at what point or how many components there are
describe voltage in a series circuitthe voltage is different at every point but the voltage across each component in the circuit adds up to the total / supply voltage VT = V1 + V2 + V3
how can you tell a circuit is parallelthere is more than one path for current to flow through
describe current in a parallel circuitcurrent in a parallel circuit splits up at different branches then combines again before going back into the supply. the sum of the current in each branch after being split is equal to the total current in the circuit. IT = I1 + I2 + I3
describe voltage in a parallel circuitthe voltage across each component in parallel is the same as the supply voltage VT = V1 = V2 = V3
describe resistance in a series circuitthe total resistance in a series circuit is the sum of the resistance of each component RT = R1 + R2 + R3
describe resistance in a parallel circuitwhen components are added in parallel the resistance of the circuit decreases to a value less than the lowest resistance value of the components. 1/RT = 1/R1 + 1/R2 + 1/R3
What is a voltage divider?a type of series circuit used to control voltages when supply voltage is divided across two resistors connected in series
what formulas can you use to calculate the voltage or resistance of any resistor in a voltage divider circuitV2 = (r2/r1+r2)xVs V1/V2 = R1/R2
how can you use a voltage divider circuitas sensing device in electronics. voltage changes across components as environmental conditions change, meaning they can be used as input devices
how does an LDR circuit workLURD consists of a voltage divider with one fixed resistor and one LDR resistance decreases when light incident on the LDR increases. The lowered resistance decreases the voltage across he LDR and in turn the voltage across the fixed resistor increases. This might turn on another device like a lamp.
how does a thermistor circuit workTURD as ambient temperature increases the resistance of the thermistor decreases. The lowered resistance decreases the voltage across the thermistor. IN turn the voltage across the fixed resistor increases. This might turn on another device like a heater.
describe how transistors work in voltage divider circuitswhen temperature decreases, the resistance of the thermistor increases. This increases the voltage across the thermistor until it is enough to switch on the base of the transistor. This causes the LED to light. This type of circuit could be used to alert drivers of icy road conditions.
do LEDs use a lot or a little currenta little current to operate normally last longer than conventional light bulbs
do LED's generate heat?no
what is done to prevent LED's becoming easily damaged by large currentsthey are placed in a voltage divider circuit with a fixed resistor known as a protective resistor