Resistance Flashcards
What is resistance?
The ratio of voltage across a conductor to the current flowing through it. Denoted by (R), measured in ohms.
State Ohm’s law.
The current flowing through a conductor is proportional to the voltage between its ends if the temperature remains contant.
What is resistance measured with?
An ohmmeter in series or parallel.
What are resistors?
Devices that attempt to impede electron flow (current).
What are the types of variable resistors?
- Rheostat
- Potentiometer
What is a rheostat?
A linear horizontal cylinder with a resistive wire coiled around it. It has three contacts, one to connect, the other two can create a fixed or variable resistance. The slider is used to vary the amount of wire used.
What is a potentiometer?
Has three contacts, one to connect, the others for fixed or varied resistance. A knob/dial is turned to adjust the resistance. This is used in more compact pieces of equipment such as dimmer dials, heating controls and volume knobs.
In resistors connected in series…
…the total resistance equals the sum of the individual resistances.
In resistors connected in parallel…
…the reciprocal of the total resistance equals the sum of the reciprocals of the individual resistances.
What are the factors affecting resistance?
- Length
- Cross-sectional area
- Material
- Temperature
How does length affect resistance?
The resistance increases as length increases.
How does cross-sectional area affect resistance?
As the radius of the cross-sectional area increases, resistance decreases. Resistance is proportional to the reciprocal of area.
How does material affect resistance?
Resistance will vary depending on which material the conductor is made from.
What is resistivity?
The constant that links resistance with length and cross-sectional area. It is denoteed by rho and measured in ohm meters.
What is a Wheatstone bridge used for?
To find the resistance value of an unknown resistor.
