warm up 3 36 the illustration shows the transcription process. what is the main purpose of the...
TRANSCRIPT
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