Resistance And Power Flashcards
What does Ohm’s law state?
That current flowing through a conductor is directly proportional to the applied voltage across it, providing the temperature remains constant, and is inversely proportional to the resistance.
What is the Ohm’s law equation?
Voltage = current x resistance V= I X R
What is resistance?
Opposition to current flow.
Explain the difference between conductors and insulators regarding their electrons.
A material with many free electrons will pass current freely (conductors), and a material with few free electrons will pass current with great difficulty (insulators).
What is resistance measured in?
OHM’S (omega sign).
What 4 things affect resistance?
Type of material
Length of conductor
The cross sectional area (CSA)
The temperature
If the length of the conductor doubles, what happens to the resistance?
It doubles.
If the CSA of the conductor decreases, what happens to the resistance?
It increases.
If material temperature increases, what happens to the resistance?
It increases.
Give some examples of insulators.
Wood Paper Rubber Mica Insulating varnish Porcelain Plastic Woven fabrics Glass
Give some examples of conductors.
Copper Brass Silver Carbon Impure water/ salt water Aluminium Mercury Gold
If the thickness of an insulator is doubled, what happens to its resistance?
It doubles.
What 3 ways can components be arranged in a circuit?
Series, parallel, series-parallel.
How do you calculate total resistance in a series circuit?
Rt = R1 + R2 + R3 etc
How do you calculate total resistance in a parallel circuit?
1/Rt = 1/R1 + 1/R2 = 1/R3 etc
Find common denominator, flip equation to find Rt.
How do you calculate total resistance in a series-parallel circuit?
Calculate the parallel part first using parallel equation, then add to the series part using series equation.
What happens to current and voltage in a series circuit?
Current flows through every component. Voltage decreases at every component.
What happens to current and voltage in a parallel circuit?
Current changes through each component, voltage remains the same through each component.
What is true of total resistance in a parallel circuit?
It will always be less than the smallest component resistance.
What is power?
Power is the rate of doing work.
What is the equation to find mechanical power and what is the measurement of mechanical power?
Power = Force x Distance / Time
Measured in horsepower.
What is the equation to find electrical power and what is it measured in?
Power = Current x Voltage
P = I X V
Measured in watts (W)
What is 1 horsepower equivalent to in watts?
746 Watts
In a standard house, what voltage is electrical equipment made to work at?
240 V
Something is rated 240 V, 60 W, explain?
It should be used in a 240 V circuit, and its power consumption is 60 W.
Explain the difference between hot and cold resistance.
Cold resistance is measured using a MIT set to Ohm’s, this is measured when no voltage is applied.
Hot resistance is calculated and is the resistance once voltage is applied.
How do you find the current rating of a motor?
Convert horsepower into watts.
Use equation: Current = Power/Voltage
