Slide 1 / 103 New Jersey Center for Teaching and Learning Progressive Science Initiative This material is made freely available at www.njctl.org and is intended for the non-commercial use of students and teachers. These materials may not be used for any commercial purpose without the written permission of the owners. NJCTL maintains its website for the convenience of teachers who wish to make their work available to other teachers, participate in a virtual professional learning community, and/or provide access to course materials to parents, students and others. Click to go to website: www.njctl.org Slide 2 / 103 Electric Field, Potential Energy and Voltage www.njctl.org Slide 3 / 103 How to Use this File Each topic is composed of brief direct instruction · There are formative assessment questions after every topic · denoted by black text and a number in the upper left. > Students work in groups to solve these problems but use student responders to enter their own answers. > Designed for SMART Response PE student response systems. > Use only as many questions as necessary for a sufficient number of students to learn a topic. Full information on how to teach with NJCTL courses can be · found at njctl.org/courses/teaching methods
Slide 4 / 103 Electric Field, Potential Energy and Voltage Click on the topic to go to that section Electric Field · *Electric Field relationship to Gravitational Field · Electric Field of Multiple Charges · **The Net Electric Field · Electric Potential Energy · Electric Potential (Voltage) · Uniform Electric Field · http:/ / njc.tl/ fv Slide 5 / 103 Electric Field Return to Table of Contents http:/ / njc.tl/ fv Slide 6 / 103 Electric Field The Electric Field starts with Coulomb's Law: This gives the force between two charges, q 1 and q 2 . Similar to the gravitational force, no contact is needed between the two charges for them to feel a force from the other charge. This "action at a distance" is best understood by assuming that each charge has a field surrounding it that affects other charges - this is called the Electric Field. http:/ / njc.tl/ fv
Slide 7 / 103 Electric Field Let's find the Electric Field due to one charge. The notation in Coulomb's Law will be modified slightly - assuming that one charge is very large - and the other charge is a small, positive test charge that will have a negligible Electric Field due to its size. The large charge will be labeled, Q, and the small charge, q, and the distance between them is r. The absolute value signs will be removed, as we will now consider the vector quality of the Force (note the arrow on the top of the F - that means that F is a vector - it has magnitude and direction). http:/ / njc.tl/ fv Slide 8 / 103 Electric Field To find the Force that the large charge exerts on the little charge, the above equation will be divided by q, and this will be defined as the Electric Field. The Electric Field now shows both the magnitude and direction of the force exerted by Q on any charge. To find the force, the Electric Field is multiplied by the charge that is being considered. http:/ / njc.tl/ fv Slide 9 / 103 Electric Field Q creates the electric field. The size of charge Q and the distance to a point determine the strength of the electric field (E) at that point. E is measured in N/C (Newtons per Coulomb). The Electric Field is represented as a group of lines that show its direction and strength - which is the Force that it would exert on a positive charge within its field. Hence, these Electric Field lines (which are imaginary, but help us visualize what is happening) originate on positive charges and end on negative charges. http:/ / njc.tl/ fv
Slide 10 / 103 Electric Field due to a Positive Charge If there is an isolated positive charge, it will create an Electric Field that points radially away from it in all directions, since a positive test charge in the field will be repelled by this charge. Electric Field Force on a small positive (electric field lines) test charge + + http:/ / njc.tl/ fv Slide 11 / 103 Electric Field due to a Negative Charge If there is an isolated negative charge, it will create an Electric Field that points radially towards it in all directions, since a positive test charge in the field will be attracted by this charge. (electric field lines) Electric Field Force on a small positive test charge - + http:/ / njc.tl/ fv Slide 12 / 103 Electric Field Direction and Magnitude The definition of the Electric Field shows that the strength of the field decreases as distance increases + This can be seen by looking at the density of the field lines. Note that the Electric Field lines are closer together (more dense) when they are closer to the charge that is generating the Field. This indicates the Electric Field is greater nearer the charge. Click here to try a simulator from PhET http:/ / njc.tl/ fv
Slide 13 / 103 Michael Faraday The electric field is attributed to Michael Faraday. Faraday was born in London in 1791. He came from a poor family. At 13, he apprenticed as a book seller and binder while also attending local lectures on philosophical and scientific topics. A member of the Royal Institute took notice of Faraday and bought him tickets to several Royal Institute lectures. In 1813, he was invited to work at the Royal Institute where he made numerous contributions to physics and chemistry. http:/ / njc.tl/ fv Slide 14 / 103 1 Find the magnitude of the electric field for a charge of 5.6 nC at a distance of 3.0 m. Answer http:/ / njc.tl/ fx Slide 14 (Answer) / 103 1 Find the magnitude of the electric field for a charge of 5.6 nC at a distance of 3.0 m. Answer [This object is a pull tab] http:/ / njc.tl/ fx
Slide 15 / 103 2 A 4.5 mC charge experiences an electrical force of 9.0 mN in the presence of an electric field. What is the magnitude of the electric field? Answer http:/ / njc.tl/ fy Slide 15 (Answer) / 103 2 A 4.5 mC charge experiences an electrical force of 9.0 mN in the presence of an electric field. What is the magnitude of the electric field? Answer [This object is a pull tab] http:/ / njc.tl/ fy Slide 16 / 103 3 If E 0 is the Electric Field generated at a distance r from a charge Q, what is the Electric Field at a distance 2r? Answer http:/ / njc.tl/ fz
Slide 16 (Answer) / 103 3 If E 0 is the Electric Field generated at a distance r from a charge Q, what is the Electric Field at a distance 2r? Answer [This object is a pull tab] http:/ / njc.tl/ fz Slide 17 / 103 4 The direction of the Electric Field can be found by using: A the direction of the gravitational force. B the direction that a positive test charge would accelerate. C the direction that a negative test charge would Answer accelerate. http:/ / njc.tl/ g0 Slide 17 (Answer) / 103 4 The direction of the Electric Field can be found by using: A the direction of the gravitational force. B the direction that a positive test charge would accelerate. C the direction that a negative test charge would Answer B accelerate. [This object is a pull tab] http:/ / njc.tl/ g0
Slide 18 / 103 5 What is the direction of the Electric Field at points 1, 2, 3 and 4? A up, right, down, left. 1 B up, left, down, right. Answer C down, right, up, left. Q+ 4 2 D down, left, up, right. 3 http:/ / njc.tl/ lo Slide 18 (Answer) / 103 5 What is the direction of the Electric Field at points 1, 2, 3 and 4? A up, right, down, left. 1 B up, left, down, right. Answer C down, right, up, left. Q+ A 4 2 D down, left, up, right. 3 [This object is a pull tab] http:/ / njc.tl/ lo Slide 19 / 103 6 What is the direction of the Electric Field at points 1, 2, 3 and 4? 1 A up, right, down, left. B up, left, down, right. Q- 4 2 C down, right, up, left. Answer D down, left, up, right. 3 http:/ / njc.tl/ g2
Slide 19 (Answer) / 103 6 What is the direction of the Electric Field at points 1, 2, 3 and 4? 1 A up, right, down, left. B up, left, down, right. Q- 4 2 C down, right, up, left. Answer D D down, left, up, right. 3 [This object is a pull tab] http:/ / njc.tl/ g2 Slide 20 / 103 7 What is the magnitude and direction of the electric field at a distance of 2.3 m due to a charge of -4.9 μC? Answer http:/ / njc.tl/ g3 Slide 20 (Answer) / 103 7 What is the magnitude and direction of the electric field at a distance of 2.3 m due to a charge of -4.9 μC? Answer Towards the charge [This object is a pull tab] http:/ / njc.tl/ g3
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