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Electric Force

Rub your feet on the carpet you dummy!!!. Electric Force. I can’t, I don’t have enough electrons…. Luke, use the force!. SWBAT describe the electric force conceptually and solve for the force mathematically. Charges. A proton has a charge of 1.60 X 10 -19 C

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Electric Force

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  1. Rub your feet on the carpet you dummy!!! Electric Force I can’t, I don’t have enough electrons… Luke, use the force! SWBAT describe the electric force conceptually and solve for the force mathematically.

  2. Charges • A proton has a charge of 1.60 X 10 -19 C • A electron has a charge of -1.60 X 10 -19 C • C = Coulomb

  3. Electric Force • The electric force depends on two things: • Charge: greater the charge on the objects, greater force • Distance between charges: closer greater force, further apart  weaker force • Follows Newton’s 3rd Law: 2 charges of any size will experience the same force as the other, but in the opposite direction.

  4. Coulomb’s Law • Charles Coulomb was the first scientist to express this force mathematically, in the 1780’s. • Fe= (kq1q2)/r2 • Notice similarity to the force of gravity • ‘r’ is the distance between the charges • ‘q’ is the 2 charges • ‘k’ is the proportionality constant • kC= 8.99 X 109 N*m2/C2 Aren’t I shocking!

  5. Practice • Note: It is usually easier to use the absolute values of the forces while solving, then decide afterwards whether it is an attractive or repulsive force. • Note: An Electron and Proton both have the same charge of 1.60 × 10-19 C. Electron is negative – Proton is positive • Practice 1: A positive charge of 6.0 x 10-6 Cis 0.03 m from a second positive charge of 3.0 x 10-6 C. Calculate the force between them and indicate if it is attractive or repulsive.

  6. Practice • Practice 2: What force exists between a positive charge of 1.5 x 10-5 C and a negative charge of -6.0 x 10-6 C, which are 5.0 cm apart.(Note the large forces involved between electric charges given in millionths of a coulomb also called a microcoulomb). • Practice 3: A negative charge of 6.0 x 10-6 C exerts an attractive force of 64.8 N on a second charge 0.05 m away. What is the sign and magnitude of the second charge?

  7. Practice • The hydrogen atom has the simplest structure of all atoms. Its nucleus is a proton (mp = 1.67 x 10-27 kg), outside of which there is a single electron (me = 9.11 x 10-31 kg) at an average separation distance of 5.3 x 10-11 m. • Solve for the electrical and gravitational forces (G = 6.67 x 10-11) between the proton and the electron in a hydrogen atom The electrical forces that subatomic particles exert on one another are so much stronger than their mutual gravitational forces, that gravitation can be completely ignored. • The electrical attraction of the proton for the electron causes the centripetal force needed to hold the electron in orbit. Find the electron’s speed.

  8. How to Solve Given/ Constants: • r= 5.3 x 10-11 m • q=1.60 X 10 -19 C (an electron is negative/ a proton is positive) • mp = 1.67 x 10-27 kg, me = 9.11 x 10-31 kg • kC= 8.99 X 109 N*m2/C2 • G = 6.67 x 10-11 N*m2/kg2 • Plug into Fe and Fg

  9. Net Electric Force • Electric force is often caused by more than 2 charged particles. • The net electric force is the vector sum of all the individual electric forces acting on an object. • This called the principle of superposition

  10. Charges in Line • Three point charges are placed on the x-axis as shown. Find the net electrostatic force on q1.

  11. Charges in a Plane • A configuration of three charges is shown. What is the net electrostatic force on q3?

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