Chapter 33: Electric field. Define an electric field. An electric field is the space around an electric charge where electric force of attraction or repulsion can be felt by another charge. Electric field around a charge is represented by electric field lines

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The direction of an electric field? The direction of the electric field at any point, is the direction of the electrical force on a small positive test charge that is placed in the field. +q0 q Small positive Test Charge will either be attracted or repelled. Charged object

What is an electric field line? Google Image Result for http://www.physicsclassroom.com/class/estatics/u8l4c13.gif

What is electric shielding? Electric shielding is the absence of electric field within a conductor because the conductor is holding static charge. The electrons within the conductor are not moving and are evenly distributed. The net force would be Zero and therefore there will be zero electric field.

100% Shielded Zero charge The electrons will stop moving towards the test charge when enough have moved to completely null the electric field inside the cylinder. Because the test charge is overall neutral, far away the field will be identical to the field from the test charge alone.

electric shielding Explain why it’s wise to remain in your car when there is thunder storm and lightning outside.

Class work/ homework Class work: Textbook page 529,# 1-10 Homework: textbook pg 686 # 1-10

Lesson 2: Describing Electric Field Consider a test charge qo inside an electric field around a large charged object as shown below. Charged object Force experienced by a test charge (F) F q qo d Positive Test Charge qo Distance between center of small Test Charge and The charged object Electric field (E) around the charged object.

Electric field formula

Electric field formula # 2 Electric field can also be calculated using the formula

example What is the electric field at a location where an electron experiences a force of 4.5 x 10-8 N?

example A moving car accumulates positive charge of 4.0 x 10-6 C. What is the magnitude and direction of the electric field 0.2 m away from the car? Soln

Class work Workbook page 202 Exercises 6-9 and page 206 #A5-A10.

Lesson 3: Electric potential Energy Warm-up: A load weighing 400 N is raised a height of 5m. Calculate the work done. What is the gravitational potential energy?

Electric potential Energy Consider a charged particle being moved towards a positively charged object. Question: Why is it not easy to reduce the separation distance between two charged objects? Separation distance between charged objects + + + Push + + + + + + + + qo + + + +q

In order to move it, External work has to be done. Answer: The small charged particle will be repelled by the large object. In order to move it, External work has to be done. When work is done on a charge, it acquires Electric potential Energy. (energy of position) Think of charging your cell phone before using it. Work Done = Electrical potential Energy.

Electric kinetic Energy When a positive charge close to a large positively charged object is released, all the electrical potential Energy becomes Kinetic Energy. (Think of using your already charged cell phone). Motion due to Repelling force + + + + qo +q + + + + + Work done to move charge = Electric potential energy = Kinetic Energy Charging cell phone → Charged cell phone → using cell phone ( law of conservation of energy)

Electric potential energy Vs Gravitational-PE Pushing charges close to a large charged object is like raising water up the cliff. + + + + + + + + + + + + + + + + +

Electric potential It is the electric potential energy per charge. Also called potential difference or voltage (V) The units of electric potential is Volts

Electric potential is constant Pushing more charges requires more work, but more electrical potential energy is generated Does the ratio of electric potential energy acquired, to the number of charge moved, change? _____________ ______________ Push + qo +q

Electric potential Any charged body has an electric potential within its electric field. Charge must not be present for there to be electric potential. When a charge is introduced in the field, that charge acquires; Electric __________ __________

Exercise Class work page 530, #31 and 32 Homework: Textbook pg 530 # 11-18

Lesson 4: Electric potential, electric field and distance between charges objects. Electric potential is proportional to the product of electric field of the charged object and the distance of separation between the test charge and the charged object. Electric potential ~ electric field • separation between charged objects (Plates)

Video on Demand - The Mechanical Universe Video on Demand - The Mechanical Universe...and Beyond - The Millikan Experiment

Class work: workbooks, Pg 203, Exercises 10-14, A10- A13.