Do Now: A 30 kg wagon is pulled East on concrete with 100 N force at a constant speed. What is the coefficient of friction for this motion?

Aim: How can we determine electric power and energy? HW:

What do electrons do as they move? As electrons travel through circuits they do WORK – as they do this they generate FRICTION and HEAT HEAT is just a type of ENERGY! Power is a RATE of ENERGY usage

P=IV Electrical Power CURRENT VOLTAGE POWER LAW The POWER built up in a circuit depends on: How many ELECTRONS are flowing through it… How much ENERGY each electron has… CURRENT VOLTAGE MORE current means more electrons producing FRICTION  MORE power MORE voltage means we push electrons HARDER  MORE power POWER LAW P=IV Measured in: WATTS

Example #1 What is the power generated in a circuit that conducts 10A of current when connected to a 15V battery? P = IV P = (10 A)(15 V) P = 150 W

Example #2 How much current is drawn by a 100W light bulb when it is connected to a 120V power supply? P = IV 100 W = I (120 V) I = 0.833 A

Combine Ohm’s Law and Power Law Recall earlier equation for power… Power Equations Combine Ohm’s Law and Power Law Recall earlier equation for power… Relate to POWER Rangers… get it? Because they are POWER and morph… like equations… yea.

Station Activity Go to the assigned station and answer the questions involving power.

Station #1 What is the power generated in a circuit with a resistance of 2.5 ohms if it is connected to a 5 volt battery? P = V2 / R P = (5 V)2 / 2.5 Ω P = 10 W

Station #2 What is the power generated in a circuit with a resistance of 300 ohms if it conducts 2 amps of current? P = I2R P = (2 A)2 (300 Ω) P = 1200 W or 1.2 kW

Station #3 How long does it take for a circuit with a 500 volt source to use 500 joules of energy at a current of 10 amperes? P = IV P = (10 A)(500 V) P = 5000 W P = W / t 5000 W = (500 J) / t t = 0.1 s

SUMMARY Watts the unit for Power? Name each version of the Power Equation (There are 4). P = IV, P = W/t, P = V2/R, P = I2R

Electric Energy

A QUICK REMINDER Power is the rate at which WORK is done per unit TIME Using the equation above, WORK will equal…

MAKING CONNECTIONS

Envelope Activity Answer the following questions inside your envelopes regarding electrical energy.

EXAMPLE #1 If an appliance is plugged into a 120V outlet and draws 10 amperes of current for ten minutes, how much energy does the appliance use?

EXAMPLE #2 Determine the resistance of an MP3 player that uses 10,000J of energy in 15 minutes when on a 9 volt battery.

EXAMPLE #3 How much current goes through a 10 ohm resistor when it uses 54 Joules of energy in one minute?

SUMMARY 1. How is electrical energy related to power? 2. Provide 2 examples from previous problems.