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 ForceDiscussion

1. Gravitational Force acts between 2 _____. 2. Electrical Force acts between 2 _____.3. In which direction does the gravitational

force act? How about the electrical force?4. Does gravity get stronger or weaker from the

center of a mass? How about electrical force?

5. Do these 2 forces seem similar?

Gravity and Electricity

Gravitational Force Electrical ForceForce between 2 masses Force between 2 chargesAttraction only Attraction & RepulsionWeaker over distance Weaker over distanceCause things to orbit Cause electrons to orbit

F kq1q2d2

k = 8.99 x 109 Nm2/C2

F Gm1m2d2

G = 6.67 x 10-11 Nm2/kg2

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

V J

C

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