Unit 5 Lecture Chapter 7 Electric Charge

Unit 5 Lecture Chapter 7

Electric Charge • Protons have + charge • Electrons have – charge • Static electricity is the accumulation of excess electric charges on an object • Law of Conservation of Charge – charge can be transferred but not created nor destroyed

Transferring charge • Conductors – allow electrons to transfer easily • Insulators – don’t allow electrons to transfer easily • Induction – rearrangement of electrons on neutral object caused by a nearby charged object

• Common conductors: • Metals • Water • • • Common insulators: Air Plastic Rubber Wood Glass

Grounding • Lightning consists of negative charges • Buildings should provide a path for the charges to reach earth • This path is a lightning rod that extends to the highest point on the building and extends to the ground

Detecting electric charge • An electroscope can detect the presence of electric charges • When the device is not charged, the metal leaves hang straight down • When charged, the leaves move away from each other

Electric Current • Diff in voltage allows charge to move from high V to low V • Electric current – flow of charges through a wire or any conductor • Electric current is measured in Amperes (A)

Batteries • A common source of voltage difference is a battery • 2 types: • 1. Dry cell- most common around the house, has a positive and negative terminal on ends • 2. Wet cell- car battery, has positive and negative terminal as knobs on top

Sockets • Another source of a voltage difference are the sockets in your house. • Most sockets in your walls provide a 120 V difference • Electric ovens and dryers need a socket with a 240 V difference

• Circuit- closed loop which allows charge to flow • Resistance - tendency for material to oppose the flow of electrons, converting electrical E into thermal E and light • Resistance is measured in Ohms • The thinner the wire, the more resistance

Equation time! • • Ohm’s Law I = current (in Amps) V = voltage (in Volts) R = resistance (in Ohms) I=V/R So greater the voltage, the greater the current Greater the resistance (distance), the smaller the current

Ohm’s Law • Calculate the voltage difference across a 25 Ohm resistor if a 0. 3 A current is flowing through it. • What happens when the voltage is doubled?

Electric Circuits 2 types: 1. Series- only one loop for the current to flow If one light bulb goes out, they all go out 2. Parallel- two or more branches for the current to flow through • If one bulb goes out, the rest stay on • •

Household Circuits • Houses are wired in parallel circuits • The fuse box or circuit breaker is the electrical headquarters of your house • If the wires get too hot from too much current flowing through them, the fuse will blow and the circuit will be broken • This protects your home from fires • Similar process in circuit breakers, except those can be reset and don’t need to be replaced like fuses

Electrical Power • Electrical energy is converted to mechanical, light, heat, etc • The rate that it is converted is electrical power • Power = current x voltage difference • P (watts) = I (amps) x V (volts) • The unit for power is W (watts)

Electrical Energy • The amount of electrical energy used depends on the amount of power required to run the appliance and how long it is used • Energy = power x time • E (k. Wh) = P(k. W) x t(h)