Please sit together in pairs: Mike A. and Heran Barney and Joe Serruto Thomas and Yiran

1. Mikhail and Grant • Valerie and Evan • Kevin and Rebecca • Ally and Katherine • Matt M. and Joe Sebek • Morgan and Quanbiao • Laura and Charlie • Lauren and Lu • Mikey O. and Ashkan • Hannah and Naichen • Jim and Dale • Nick and Disha • Ben and Efrain • Nik and Da • Please sit together in pairs: • Mike A. and Heran • Barney and Joe Serruto • Thomas and Yiran • Glenn and Steve T. • Ann and Joey B. • Johnny and Andrea • Korey and Stephen H. • Will and Qihan • Michael W. and Nicole • Zach and Ed • Casey and Zhenmin • Audrey and Taehoon • Lisette and Shenheng • Erica and Matt R. Phys 150 Lecture 12

2. Announcements • Exam 1 solutions available online. • Homework 6 is due on Monday, Oct. 15 at midnight. Phys 150 Lecture 12

3. Power Bulbs • 100 Watt incandescent light bulb • Most of the power is producing heat, not light • 26 Watt Compact Fluorescent Light (CFL) • Same light output with ¼ the energy use! • Light Emitting Diode (LED) • About same energy efficiency as CFL Phys 150 Lecture 12

4. Chapter 6 – Electricity and Magnetism • Electricity Van de Graaff Water Phys 150 Lecture 12

5. i>clicker question Chemical reactions produce voltages that are typically • 1 volt • 100 volts • 10,000 volts • 1 million volts Phys 150 Lecture 12

6. i>clicker question Chemical reactions produce voltages that are typically • 1 volt = 1 eV per electron • 100 volts • 10,000 volts • 1 million volts • Alkaline battery = 1.5 volts • 9 volt battery = 6 alkaline batteries • Car battery (Lead – Acid) = 6 2-volt batteries • Lithium ion battery = 3.6 volts • NiMH battery = 1.2 volts Lemon Phys 150 Lecture 12

7. i>clicker question When you get an electric shock from a door knob, the voltage is typically • 1 volt • 100 volts • 10,000 volts • 1 million volts Phys 150 Lecture 12

8. i>clicker question When you get an electric shock from a door knob, the voltage is typically • 1 volt • 100 volts • 10,000 volts – actually, more like 50,000 volts • 1 million volts • Sparks - 30,000 volts/cm (in air) • A spark is an electric current in air Wimshurst Phys 150 Lecture 12

9. i>clicker question Resistance model The resistance of a conductor • increases with increasing temperature • decreases with increasing temperature • is independent of temperature • It depends on the material Phys 150 Lecture 12

10. i>clicker question The resistance of a conductor • increases with increasing temperature • decreases with increasing temperature • is independent of temperature • It depends on the material Platinum Semiconductor Phys 150 Lecture 12

11. i>clicker question The voltage from an electrical outlet is • a constant 110 volts • a constant 220 volts • varying (average 110 volts) • varying (average 220 volts) Phys 150 Lecture 12

12. i>clicker question The voltage from an electrical outlet is • a constant 110 volts • a constant 220 volts • varying (average 110 volts) • varying (average 220 volts) – Europe (50 Hz) • Varies 60 times/sec (60 Hz) • Alternating current (AC) vs Direct current (DC) Light string Phys 150 Lecture 12

13. i>clicker question We use AC for electric power distribution because • it makes it easy to change voltage • it is less dangerous • most devices require AC current • it is cheaper Phys 150 Lecture 12

14. i>clicker question We use AC for electric power distribution because • it makes it easy to change voltage • it is less dangerous • most devices require AC current • it is cheaper • High voltage -> Low current (P=IV) • Low current -> Less power loss to heat (I2R) Power lines Fuse Phys 150 Lecture 12

15. i>clicker question An electric spark of 50,000 volts may not hurt you if • the current is low • the current lasts a very short time • the power is low • Any of the above Phys 150 Lecture 12

16. i>clicker question An electric spark of 50,000 volts may not hurt you if • the current is low • the current lasts a very short time • the power is low • Any of the above • P = IV • Energy = P x time Phys 150 Lecture 12