Warm Up 3 36 The illustration shows the transcription process. What is the main purpose of the structure labeled W? F Carrying instructions for protein synthesis G Transforming into a protein H Replacing damaged DNA J Passing traits to offspring

Electric & Gravitational Fields and Electric Potentials

Gravitational vs Electrical Force Discussion Gravitational Force acts between 2 _____. Electrical Force acts between 2 _____. In which direction does the gravitational force act? How about the electrical force? Does gravity get stronger or weaker from the center of a mass? How about electrical force? Do these 2 forces seem similar?

Gravity and Electricity Gravitational Force Electrical Force Force between 2 masses Force between 2 charges Attraction only Attraction & Repulsion Weaker over distance Cause things to orbit Cause electrons to orbit G = 6.67 x 10-11 Nm2/kg2 k = 8.99 x 109 Nm2/C2

Force Fields in Physics Force Fields are just areas with forces. Gravitational Field – Area where the force of gravity pulls on an object Electric Field – Area where an electric force can push or pull an object

Repulsion or Attraction? Visualization of an electric field Polarized thread in oil

Attraction or Repulsion? Line model

Force Fields in Physics Force fields are drawn with lines The lines represent the direction positive charge would accelerate if placed in the field. The result is lines start from a positive charge and end at a negative charge

Force Fields in Physics Force fields are drawn with lines The density of lines represent magnitude

Electrical Potential Energy Think about trying to bring together 2 magnets at their North poles. How much force does it take for you to bring them together? At the beginning versus when they are really close?

Electrical Potential Energy Electrical Potential Energy – Energy required to keep a charge from moving in an electric field. Strong field + strong charge + short distance = high Electrical Potential Energy When the charge is released, that potential energy is transformed to kinetic energy

Electric Potential Electric potential = “electric potential energy”/”charge” SI unit for Electric Potential is the “volt”, V

Misconceptions of the Volt High Voltage is deadly Van de Graaff generators can easily generate 50,000 V High potential energy but very little charge

Sample Problem If 20. J of work is required to move 4.0 C of charge in a uniform electric field, the electric potential will be _____. A) 80. V B) 5.0 V C) 0.0 V D) 100 V

Exit Ticket 2 Consider two charged objects. One carries a charge of 1.8 x10-6 C When the two are separated by a distance of 0.9m, there is a force of 2.7 N between them. What is the charge on the second object?

Warm Up 4

Electric Potential Energy Electric Potential Energy (ePE) is due to a charge’s location in an electric field ePE is the amount of work needed to move a charge to that location Similar to gravitational potential energy depends on the height of an object The amount of charge you are moving does not matter

Lightning High Electric Potential is created by friction and air currents in the clouds Clouds become polarized, usually bottom of the cloud is negative Polarized cloud induces the ground to be polarized Lightning occurs to neutralize the charge imbalance

Electric Shielding Why is it safe to drive stay inside a car during a lightning storm? Excess charges only coat the surface of an object Object’s normal electrons force the extra electrons to stay outside Inside of the car remains neutral Same with the inside of a Van de Graaff generator

Lab – Mapping Electric Potential Groups of up to 3 You will measure the electric potential difference with a volt meter Measure 36 (6 x 6) points around the positive terminal Measure 6 points from the negative terminal to the positive terminal Draw contour map at 0.5 V intervals Turn in drawing