Resistance Flashcards
What is the SI unit of resistance?
Ohm, named after German physicist Georg Simon Ohm.
What is resistance defined as?
The resistance of a substance is defined as the ratio of the voltage drop across it to the current flowing through it: R=V/I
Does the resistance of a conductor increase or decrease when the temperature rises?
The resistance of a substance increases with temperature.
What is a resistor used for?
A resistor is used to control the current flowing through, and the voltage drop across, parts of a circuit. They have constance resistances.
What are the three types of resistors made from?
Composition resistors are made of semiconductor carbon.
Wire wound resistors are made of a coil of fine wire made of a resistance alloy (such as nichrome).
Metal film resistors are made of a glass or pottery tube coated with a thin film of metal.
What do the first two coloured bands represent on a resistor?
The first two digits of the value of resistance.
What does the third coloured band on a resistance represent?
The power which the first two digits are multiplied by.
What does the fourth coloured band on a resistor represent?
The manufacturing tolerance percentage.
What is Ohm’s law?
The equation V=IR, which shows the current is proportional to the voltage. R is equal to the constant gradient of the line.
What is an ohmic device?
An ohmic device is a device that under constant physical conditions (such as temperature), had a resistance that is constant for all currents that pass through it.
What is a non-ohmic device?
A non-ohmic device has a resistance that is different for different currents passing through.
What is a diode?
A diode is a device that allows current to pass through it in one direction.
What is an LED?
A Light-Emitting Diode is a small semiconductor that emits light when a current passes through it.
What is a thermistor?
A thermistor is a device that has a resistor which changes with a change in temperature. They are made of a mixture of semiconductors so they conduct electricity in both directions.
