Section 2

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Transcript Section 2

 As you lift an object off the ground, you are increasing its potential energy  ◦ ◦ Same is for electric potential  Electric potential ( Δ V) Work done moving a test charge in an electric field by dividing the magnitude of the test charge  Δ V = W / q (Work is the Potential energy need to remove the charge over some distance = joules) Measured in joules /coulomb (J/C = Volt (V))

   Work is required to push a charged particle against the electric field of a charged body.

EPE is the energy a charge particle possesses because of its location in an electric field.

If the particle is released it will accelerate away turning the EPE into kinetic energy.

   ◦ ◦ ◦ If you apply 150 J of work to move a positive charge of 3.5 x 10 -6 C from a negative plate, what is the electric potential difference?

Known ◦ ◦ Work on q = 150 J q=3.5 x 10 -6 C Unkown Δ V Δ V = W / q = 150 J / 3.5 x 10 -6 = C

 ◦ Electric Potential Smaller when two unlike charges are closer together ◦ Larger when two like charges are

   ◦ Uniform electric force and field made by placing 2 large conducting plates parallel to each other Direction is from + plate to –plate Potential difference, Δ V, between 2 points a distance (d) apart, in a uniform field (E) Δ V = Ed

   2 Parallel plates are given opposite charges. A voltmeter measures the EPD to be 60.0 V. The plates are 3.0 cm apart. What is the magnitude of the electric field between them?

Known ◦ ◦ ◦ Δ V = 60.0 V D = 0.030 m Unkown E = ???

   E = V / d = 60.0 V / 0.030 m = 2.0 x 10 3 N/C

   ◦ ◦ Storing energy in an electric field Leyden Jar Developed by Dutch physicist Pieter Van Musschenbroek Used by Ben Franklin to store charges from lightning Version is still used today: Capacitor

  Ratio of charge stored to electric potential difference: called Capacitance, (C) ◦ ◦ Capacitor designed to store electric charges and energy ◦ Made of two conductors separated by an insulator ◦ Capacitance = charge / electric potential difference C = q / Δ V Measured in Coulomb per volt (C/V) or 1 Farad (F)

   ◦ A sphere has an eletric potential difference between it and Earth of 60.0 V when it has been charged to 3.0 x 10 -6 C. What is the capacitance?

Known ◦ V = 60.0 V ◦ q = 3.0 x 10 -6 Unknown C = ???

    C = q / Δ V = 3.0 x 10 -6 / 60.0 V = 0.00000005 F = 0.05 µF

Examples:

crank/shake flashlight, computer keyboards, flashes in cameras, electronics.