Electric ChargeFacts about charge:• There are 2 types basically, positive (protons) and negative (electrons)• LIKE charges REPEL and OPPOSITE charges ATTRACT• Electrostatic forces – both attractive and repulsive forces – are the foundation of our existence! • They are responsible for holding the building blocks of matter (atoms and molecules) together in perfect balance!
Electric Charge – The specifics •The symbol for CHARGE is “q” •The unit is the COULOMB (C), Some important constants: named after Charles Coulomb •If we are talking about a SINGLE charged particle such as 1 electron or 1 proton we are referring to an ELEMENTARY charge and often use, e , to symbolize this.Particle Charge MassProton 1.6x10-19 C 1.67 x10-27 kgElectron 1.6x10-19 C 9.11 x10-31 kgNeutron 0 1.67 x10-27 kg
Charge is “CONSERVED” Charge cannot be created or destroyed only transferred from one object to another. Even though these 2 charges attract initially, they repel after touching. Notice the NET charge stays the same. These are examples of IONS – they have a net charge not equal to zero. • atoms gain more electrons OR • Lose electrons
Conductors and InsulatorsThe movement of charge is limited by the substance the charge is trying to pass through. There are generally 2 types of substances.Conductors: Allow charge to move readily though it.Insulators: Restrict the movement of the charge Conductor = Copper Wire Insulator = Plastic sheath
Which one is which?!!!One of these isolated charged spheres is copper and the other is rubber. The diagram below depicts the distribution of excessnegative charge over the surface of two spheres. Label which is which and support your answer with an explanation.
Charging and DischargingThere are basically 2 ways you can charge something.2. Charge by friction3. Induction “BIONIC is the first-ever ionic formula mascara. The primary ingredient in BIONIC is a chain molecule with a positive charge. The friction caused by sweeping the mascara brush across lashes causes a negative charge. Since opposites attract, the positively charged formula adheres to the negatively charged lashes for a dramatic effect that lasts all day.”
Triboelectric series • Tells us about the electron affinity (aka an object’s “love”) of electrons • To the right: objects higher up tend to give up electrons easily • Have lower electron affinity • So if you rub an object at the top again an object on the bottom, you will get a transfer of charge!
Induction and Grounding The second way to charge something is via INDUCTION, which requires NO PHYSICAL CONTACT.
Induction and Grounding The second way to charge something is via INDUCTION, which requires NO PHYSICAL CONTACT.We bring a negatively charged rod near a neutral sphere. The protons in the spherelocalize near the rod, while the electrons are repelled to the other side of the sphere. Awire can then be brought in contact with the negative side and allowed to touch theGROUND. The electrons will always move towards a more massive objects to increaseseparation from other electrons, leaving a NET positive sphere behind.
Electroscope• The electroscope typically consists of a conducting plate or knob, a conducting base and either a pair of conducting leaves or a conducting needle. • It can be used to determine charge!
Test your KNOWLEDGE• Suppose that a negatively charged balloon is used to charge an electroscope. Explain in terms of electron movement what is happening in each step.
Electric ForceThe electric force between 2 objects is symbolic of the gravitational force between 2 objects. RECALL: 1 Fgα Mm Fg α 2 r 1 qq FE α q1q2 FE α FEα 1 2 2 r2 r k = constant of proportionality Nm 2 k = Coulomb constant = 8.99 x109 2 C q1q2 FE = k 2 → Coulomb s Law r
Example: Coulombs Law• Two balloons are charged with an identical quantity and type of charge: -6.25 nC. They are held apart at a separation distance of 61.7 cm. • How many electrons are contained within one of the charged balloons? • Determine the magnitude of the electrical force of repulsion between them. 3.9x1010 electrons 9.4x10-7 N repulsive force
ExampleCalculate the separation distance between a 12C charge and a 6Ccharge is the electric force between them is 136.5 N q1q2 q1q2 Fe = k 2 → r = k r Fe (12)(6) r = (8.99 ) 9 = 68,900.31 m (136.5)