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Here we have an apple that is at a height h above the Earths surface.

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The apple has a potential energy equal to

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Anywhere along the dotted line the apple has the same height, therefore the same potential energy.

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This line that has the same potential is called an line.

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This line that has the same potential is called an line.

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For any object there is an infinite number of lines.

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Here we show some of the different lines.

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If we moved the apple along one of these lines

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there would be no change in potential energy therefore no work would be done.

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Once again, there was NO WORK done in moving the apple along the from point A to point B.

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We also know that if we raise an apple above the Earth and let it go, it will fall.

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The direction that the apple accelerates tells us the direction of the gravitational force.

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The direction of the gravitational force and the pattern of equilpotential lines give us a view of the. By Richard J. Terwilliger

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around the Earth.

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means that there will be a gravitational force on an object if it is placed in the field.

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Could this model also work with

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And how would we deal with two different net charges?

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Lets start with an object that has a NET NEGATIVE charge.

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Placing a test charge in the vicinity of this net negative charge and noticing if it experiences a force will tell us if there is an Electric Field around the charge.

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It will also tell us the direction of the Electric Field.

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The test charge is always defined as

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Therefore the test charge has a force acting on it the net negative charge.

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This is the direction of the

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Moving the test charge around the net negative

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and plotting the direction of the force will show us the field surrounding the charge.

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This positive test charge if free to move will fall towards the net negative charge.

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The positive test charge has no potential energy at this point.

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To pull the positive test charge away from the negative we must do work on the positive test charge.

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This work is equal to the potential energy at that point.

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So similar to the equipotentials surrounding the Earth,

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we have equal potentials surrounding the net negative charge.

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If the charge moves along the equipotential there is no work done.

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By Richard J. Terwilliger

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If the charge moves along the equipotential there is no work done. By Richard J. Terwilliger

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If the charge moves along the equipotential there is no work done.

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By Richard J. Terwilliger

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If the charge moves along the equipotential there is no work done.

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We now know the direction of the force and the pattern of equipotentials around the net negative charge.

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Notice the lines of force are at right angles to the equipotential lines. 90 o

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We can now predict the electric lines of force and the equipotential lines around a charge.

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A positive test charge placed near the net positive charge will experience a force outward.

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Therefore the electric field surrounding the net positive radiates out away from the positive.

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And the equipotential lines must cross these force lines at right angles forming concentric circles.

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Notice the force lines never cross each other and the equipotential lines never cross.

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So we now know what the fields look like around either a positive or negative charge

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What would the electric field lines and the equipotential lines look like around two charges?

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One negative and one positive.

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First we place our positive test charge in the field and determine the direction of the force on the test charge.

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The test charge is repelled away from positive and attracted toward the negative.

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Now move the test charge to a new position and determine the direction of the force.

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Keep moving the test charge and determine the direction of the force at each new position.

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If we place the test charge at the position shown,

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The test charge will experience a large force pushing it away from the positive charge and

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A very small force pulling it towards the negative charge.

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The electric field, at this point, would be the resultant of these two forces.

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Move the test charge and again find the resultant.

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Here the test charge is further away from the positive charge so the force is smaller.

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Move the test charge and again find the resultant force.

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Keep repeating until you have the pattern for the electric field line, the line of force.

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Once more.

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Connecting all of these arrows gives us the electric field line.

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From here we can finish the pattern.

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Now draw in the Remember, they never cross each other and must cross the force lines at right angles.

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What does the Electric Force lines and Equipotential lines look like between parallel plate charges?

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Lets check it out!

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First well start with two parallel plates.

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Next well charge one plate net negative and the other plate net positive.

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To determine the direction of the electric field well place the test charge between the plates.

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Remember the test charge?

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Is the test charge positive or negative? CLICK on YOUR ANSWER

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Hello? McFly!

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The electric field direction is determined using a net test charge

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A positive charge placed between the two parallel plates

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will be forced away from the positive plate and towards the negative plate.

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Therefore the electric field direction between two parallel charged plates is away from the positive plate and towards the negative plate.

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And the equipotential lines are perpendicular to the force lines.

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Topic 9.3 Electric Field, Potential, and Energy

Topic 9.3 Electric Field, Potential, and Energy

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