Aim How do we determine the power in
- Slides: 18
Aim: How do we determine the power in a circuit? HW: Problem Set
Ohm’s Law Applied • A 10 volt battery is connected to a circuit, allowing 5 amperes of current flow. Calculate the resistance of the circuit.
What do electrons do as they move? As electrons travel through circuits they do WORK – as they do this they generate FRICTION and HEAT is just a type of ENERGY! Power is a RATE of ENERGY usage
Electrical Power The POWER built up in a circuit depends on: How many much ELECTRONS ENERGY are each flowing electron through has… it… MORE current voltage means more weelectrons push electrons producing FRICTION HARDER MORE power POWER LAW P=IV Measured in: WATTS
Example #1 • How much current is drawn by a 100 W light bulb when it is connected to a 120 V power supply? P = IV 100 W = I (120 V) I = 0. 833 A
Example #2 • 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=W/t P = (10 A)(500 V) 5000 W = (500 J) / t P = 5000 W t = 0. 1 s
Power Equations Combine Ohm’s Law and Power Law Recall earlier equation for power…
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 = V 2 / 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 = I 2 R P = (2 A)2 (300 Ω) P = 1200 W or 1. 2 k. W
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 120 V outlet and draws 10 amperes of current for ten minutes, how much energy does the appliance use?
EXAMPLE #2 • Determine the resistance of an MP 3 player that uses 10, 000 J 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. 3. How do we measure current and potential difference in a circuit?
