Electrical Energy And Power

Question 1

What is Power?

Answer 1

Is the rate of doing work

Question 2

What is Power measured in?

Answer 2

Watts (W)

Question 3

What is the Power equation?

Answer 3

P = E/t

Question 4

In a electrical circuit what is E that is part of P = E/t?

Answer 4

Work done moving a charge

Question 5

What is the Power equation for electrical circuits?

Answer 5

P = IV

Question 6

Why does the Power = IV equation make sense?

Answer 6

• Potential Difference is defined as the work done per coulomb
• Current is defined as the number of Coulombs transferred per second
• So P.D x Current is work done per second, i.e Power

Question 7

Combining P = IV and V = IR together can give you more equations such as?

Answer 7

P = I*2 x R

P = V*2 / R

Question 8

Energy is easy to calculate if you know the […….]

Answer 8

Power

Question 9

If you want to work out total energy transferred what is the equation we use?

Answer 9

E = Pt

Question 10

By substituting in other equations what can E =Pt be?

Answer 10

W = IVt
Or
W = (V*2 / R)t
Or
W = I*2 x R x t

Question 11

How do you investigate the power output of an electric motor?

Answer 11

• Attach mass to the motor as shown and connect the motor to the circuit as shown
• Record the time taken for the motor to raise the mass a set distance (using a stopwatch and meter rule)
• Calculate the work done against gravity using ΔEgrav = mg Δh
• Calculate the Power output of the motor using P = W/t
• Can also investigate efficiently taking P.D reading and Current readings to calculate the Power using P = IV
• Use the equation Efficiency equation Efficiency = (useful power output / Total power input)
• Could also investigate, using this apparatus, to investigate wether the power input and power output of the motor varies with the laid attached to it by varying the mass.