P1a Topic 10Internal

Assessment

Diagram of Electric Motors

Coil of Copper WireMagnet

Split-Ring Commutator

Energy Transfers

1. List the energy transfers for the following machines.

2. Identify the useful energy output and the wasted energy output.

a) Fireworkb) Battery-Operated Radioc) Electric Motord) Light Bulbe) Hairdryer

Units of Measurement in Physics

• Voltage ( )

• Current ( )

• Resistance ( )

• Power ( )

• Charge ( )

• Energy ( )

• Energy ( )

Physics Formulae

• Voltage = Current x Resistance– V = I x R

• Power = Current x Voltage– P = I x V

• Charge = Current x Time– Q = I x t

• Energy = Charge x Voltage– E = Q x V

• Energy = Current x Voltage x Time– E = I x V x t

• Energy = Power x Time– E = P x t

• Cost of Electricity = Power x Time x Cost of 1 kWh

Which line of best fit would you use to show this pattern?

Best curve.

What would an estimate for 7V be?

Why is this only an estimate?

• Capacity (batteries) = Current x Time– Capacity = I x t

• Payback Time = Installation Cost

Annual Saving

• Efficiency = Useful Output x 100

Total Input

Voltage, Current, and Energy

• To transfer a lot of electrical energy you either need a high voltage or a high current– P = I x V

• The problem with high current is the loss (as heat) due to the resistance of the cables– P = I2 x R

• It is much cheaper to increase the voltage• This keeps current low, meaning less wasted

energy (higher efficiency)

Practical Skills

• Variables– Independent and Dependent– How are they set up in a table? on a graph?

• Emphasis on ‘accurate and reliable results’– Concept of fair testing– Repeating the experiment

• Tables and Graphs– How are anomalies identified?– How can the problem of anomalies be

eradicated?

• Always draw a scatter graph unless told otherwise– Lines / Curves of Best Fit always included

• Label axes / Column headings with correct units

Paying up

• Work sheet

• P1a. 10.5 (1 and 2)

What are the benefits of using energy more efficiently?