Download - Chapter 21 Physics
Chapter 21 Physics
Electric charges
• Two types of Electric charge one called positive and the other negative.
• When charges are the same in an object it is neutral.
• An object can lose or gain an electric charge therefore it has a net charge
Charge stability
• Static electricity is a tiny imbalance of charges and can be transferred easily to help restore a zero charge.
• Structure of an atom need to know the charge in coulombs and the mass of the parts of an atom.
Parts of the atom
Mass and charges• Proton has a mass of • 1.673 x 10-27 kg
• Proton has a charge of + 1.602 X 10 -19 C
• Neutron has a mass of 1.675 X 10-27 kg
• Neutron has a charge of 0
Mass and charges• Electron has a mass of 9.109
X 10-31 kg
• Electron has a charge of -1.602 X 10-19 C
• Coulomb was named in honor of Charles Coulomb who made the first fine measurement between the forces between charges.
• Coulomb = C and has a charge of 6 X 10 18 Protons or electrons
• The unit of C can apply to both positive and negative charge
Electric forces
• Like charges repeal each other and unlike charges attract each other
• Works with electroscope
Electric current
• Formula is:• I = q/t• I = current in amps• . Q = charge that flows• . t = Time for charge to flow in seconds
Electric current
• Say that current is the movement of electric charge through a circuit.
• Eg. A current of 10 amperes means that 10 amperes of charge flow through the wire every second.
• Drift velocity is caused by an applied voltage added to random bouncing thus causing electrical current.
Conductors and insulators
electrons in a conductor with current move opposite the current flow
Electrons in an insulator do not move at all
Electrons in a semiconductor has a few free electrons to move with the current flows.
Static electricity and Polarization
• Charging by friction causes the attraction of objects
• Polarization of objects causes the insulated material to have electrons go to one side.
• Conductors the entire object becomes polarized.
Coulomb’s law
• F = K q1 q2/ r2
• F = force in Newton's • K = a constant 9 X 109 N m2 / C2
• . q = charges• . r = Distance (m)
Coulomb’s Law
• The force between charges is directly proportional to the magnitude or amount of each charge.
• The force between charges is inversely proportional to the square of the distance between them. Or the inverse square law goes into effect.
Coulomb’ s law
• Used to calculate point charges
• Electric forces always occurs in pairs according to Newton’s third law of motion
Electric fields
• Gravitational field strength = F = mg
• Electric field strength = F= qE• F = Force• . q = charge• E = electric field• Strength of the field = N/kg
Information
• One volt is one joule/coulomb• A joule is equal to a newton-meter• Newton/C = one volt per meter
Capacitors
• Is a storage device for electric charges• Can be charged by connecting it battery• Can be discharged by connecting It to any
closed circuit that allows current to flow
Capacitors
• The current flowing into or out a particular capacitor depends on four things:
• 1. The amount of charge already in the capacitor.
• 2. The voltage applied to the capacitor by the circuit.
• 3. Any circuit resistance that limits the current flowing in the circuit
Capacitors
• 4. The capacitance of the capacitor.
• The amount of charge in a capacitor depends on the following:
• 1. The voltage applied to the capacitor• 2. The insulating ability of the material
between the positive and negative plates
Capacitors
• 3. The area of the two plates ( larger > smaller)• 4. The separation distance between the plates
Capacitance
• . q = CV• . q = Charge (C) • C = Capacitance C?V• V = voltage (V)