p3 Flashcards
Static electricity:
- When certain insulating materials are rubbed together, negatively charged electrons are scraped off one material and dumped on the other.
- This will leave the materials electrically charged, with a positive static charge on one and an equal negative static charge on the other.
- Which way the electrons are transferred depends on the two materials involved.
- If enough charge builds up, it can suddenly move, causing sparks or shocks.
Similar charges…
…repel.
Opposite charges…
…attract.
What is an electric field?
An electric field is the space surrounding any electric charge, where its effects can be felt.
What type of circuit can current flow round?
Current can only flow round a closed circuit.
What is electric current?
Electrical current is the rate of flow of electrical charge.
What is potential difference?
Potential difference (or voltage) is the driving force that pushes the charge round. Its unit is volt.
What is Resistance?
Resistance is anything that resists the flow of charge. All circuit components have a resistance, but you can usually ignore the resistance from wires connecting components as it’s too small. Unit: Ohm
Charge (coloumbs,C)=
current (A) x time (s)
Potential difference (V)=
current (A) x resistance
What does the term I-V characteristic refer to?
The term “I-V characteristic” refers to a graph which shows how the current (I) flowing through a component changes as the potential difference (V) across it is increased.
What is a diode?
A diode is a special device made from semiconductor material such as silicon, it lets current flow freely through it in one direction, but not in the other.
What does LDR stand for?
LDR stands for “Light dependent resistor” and it is a resistor that’s dependent on the intensity of light. So at a constant light level, its resistance is constant.
What is a thermistor a type of?
A thermistor is a type of temperature dependent resistor.
- In hot conditions the resistance of a thermistor drop.
- In cooler conditions, the resistance goes up.
What can sensing circuits be used for?
Sensing circuits can be used to turn on or increase the power to components depending on the conditions that they are in.
What is potential difference between 2 points equal to?
Potential difference between two points is equal to the work done per unit charges flowing between those two points.
Potential difference=
work done (energy transferred) / charge
Energy transferred (work done)=
charge x potential difference
What do power ratings on devices tell you?
The power ratings tell you the rate that energy is transferred to them from a power supply. Some of this energy will be transferred to its surroundings though.
What is power measured in?
Watts (W)
Power(W)=
energy(j) / Time(s)
Power(W)=
potential difference(V) x current (A)
Power(W)=
current^2 x resistance
In a series circuit the different components are…
…end to end, between the +ve and -ve terminals of the power supply.
