| what is done to prevent LED's becoming easily damaged by large currents | they 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 of | three parts of two types of semi conductor material. N type and P type |
| name one type of semiconductor material | silicon |
| what must happen in order for current to flow through the NPN transistor - in detail | where 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 transistor | base
collector
emitter |
| how is an npn transistor set up | with 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 on | the 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 for | metal oxide semiconductor field effect transistor |
| what are the different parts of a MOSFET | gate, source, drain |
| how can you switch on a MOSFET | a positive input voltage greater than 2V applied to the gate. |
| describe in detail how a MOSFET is switched on | a 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 series | the components are connected one after the other in the circuit |
| describe current in a series circuit | current 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 circuit | the 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 parallel | there is more than one path for current to flow through |
| describe current in a parallel circuit | current 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 circuit | the voltage across each component in parallel is the same as the supply voltage
VT = V1 = V2 = V3 |
| describe resistance in a series circuit | the total resistance in a series circuit is the sum of the resistance of each component
RT = R1 + R2 + R3 |
| describe resistance in a parallel circuit | when 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 circuit | V2 = (r2/r1+r2)xVs
V1/V2 = R1/R2 |
| how can you use a voltage divider circuit | as 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 work | LURD
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 work | TURD
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 circuits | when 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 current | a 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 currents | they are placed in a voltage divider circuit with a fixed resistor known as a protective resistor |
