Resistance And Power

Question 1

What does Ohm’s law state?

Answer 1

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.

Question 2

What is the Ohm’s law equation?

Answer 2

Voltage = current x resistance
V= I X R

Question 3

What is resistance?

Answer 3

Opposition to current flow.

Question 4

Explain the difference between conductors and insulators regarding their electrons.

Answer 4

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).

Question 5

What is resistance measured in?

Answer 5

OHM’S (omega sign).

Question 6

What 4 things affect resistance?

Answer 6

Type of material
Length of conductor
The cross sectional area (CSA)
The temperature

Question 7

If the length of the conductor doubles, what happens to the resistance?

Answer 7

It doubles.

Question 8

If the CSA of the conductor decreases, what happens to the resistance?

Answer 8

It increases.

Question 9

If material temperature increases, what happens to the resistance?

Answer 9

It increases.

Question 10

Give some examples of insulators.

Answer 10

Wood
Paper
Rubber
Mica
Insulating varnish
Porcelain
Plastic
Woven fabrics
Glass

Question 11

Give some examples of conductors.

Answer 11

Copper
Brass
Silver
Carbon
Impure water/ salt water
Aluminium
Mercury
Gold

Question 12

If the thickness of an insulator is doubled, what happens to its resistance?

Answer 12

It doubles.

Question 13

What 3 ways can components be arranged in a circuit?

Answer 13

Series, parallel, series-parallel.

Question 14

How do you calculate total resistance in a series circuit?

Answer 14

Rt = R1 + R2 + R3 etc

Question 15

How do you calculate total resistance in a parallel circuit?

Answer 15

1/Rt = 1/R1 + 1/R2 = 1/R3 etc

Find common denominator, flip equation to find Rt.

Question 16

How do you calculate total resistance in a series-parallel circuit?

Answer 16

Calculate the parallel part first using parallel equation, then add to the series part using series equation.

Question 17

What happens to current and voltage in a series circuit?

Answer 17

Current flows through every component. Voltage decreases at every component.

Question 18

What happens to current and voltage in a parallel circuit?

Answer 18

Current changes through each component, voltage remains the same through each component.

Question 19

What is true of total resistance in a parallel circuit?

Answer 19

It will always be less than the smallest component resistance.

Question 20

What is power?

Answer 20

Power is the rate of doing work.

Question 21

What is the equation to find mechanical power and what is the measurement of mechanical power?

Answer 21

Power = Force x Distance / Time

Measured in horsepower.

Question 22

What is the equation to find electrical power and what is it measured in?

Answer 22

Power = Current x Voltage
P = I X V
Measured in watts (W)

Question 23

What is 1 horsepower equivalent to in watts?

Answer 23

746 Watts

Question 24

In a standard house, what voltage is electrical equipment made to work at?

Answer 24

240 V

Question 25

Something is rated 240 V, 60 W, explain?

Answer 25

It should be used in a 240 V circuit, and its power consumption is 60 W.

Question 26

Explain the difference between hot and cold resistance.

Answer 26

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.

Question 27

How do you find the current rating of a motor?

Answer 27

Convert horsepower into watts.

Use equation: Current = Power/Voltage