Physics Chapter 23

Electric potential difference

Example: Water from a higher reservoir to a lower one—flow continues until no difference No flow of charge occurs when potential difference is zero.

Electric potential difference

A battery or generator can maintain a steady flow of charge. Work is done in pulling negative charges apart from positive ones. Electromagnetic induction at the generator terminals provides the electrical pressure to move electrons through the circuit.

Commercial electricity in North America

Alternating current (ac) 60 cycles per second (60 hertz) Voltage is 120 V

Conductor

Any material having free charged particles that easily flow through it when an electric force acts on them

Circuits

Any path along which electrons can flow from the negative terminal to the positive terminal

Circuit breaker

Automatic switch that turnsoff when the current is excessive

Difference in potential between two points

Charges in conductor flow from higher potential to lower potential. Flow of charge persists until both ends of conductor reach the same potential. Maintained for continuous flow by pumping device.

Flow of charged particles In metal wires

Conduction electrons are charge carriers that are free to move throughout atomic lattice. Protons are bound within the nuclei of atoms.

Electric shock

Damaging effects of shock result from current passing through the body. Electric potential difference between one part of your body and another part depends on body condition and resistance, which can range from 100 ohms to 500,000 ohms.

Which of these statements is true? A. Electric current is a flow of electric charge. Electric current is stored in batteries. Both A and B are true. Neither A nor B are true.

Electric current is a flow of electric charge Voltage, not current, is stored in batteries. The voltage will produce a current in a connecting circuit. The battery moves electrons already in the wire, but not necessarily those in the battery.

Alternating Current (ac)

Electrons in the circuit are moved first in one direction and then in the opposite direction, alternating to and fro about fixed positions. This is accomplished by alternating the polarity of voltage at the generator or other voltage source.

Alternating current

Electrons oscillate to and fro around fixed positions. Movement is produced by a generator or an alternator that switches the signs of charge periodically. Commercial ac circuits are used in most residential circuits throughout the world and can be stepped up to high voltage for transmission over great distances with small heat losses and stepped down where energy is consumed.

Factors affecting electrical resistance (continued) Temperature

Factors affecting electrical resistance (continued) Temperature

Direct current (dc)

Flows in one direction only. Electrons always move from the negative terminal toward the positive terminal.

Factors affecting electrical resistance

Inversely proportional to cross-sectional area thin wires, more resistance than thick wires Directly proportional to length doubling the length, doubles the resistance Material rubber—much more resistance than copper of the same size

Speed of Electrons and Source of Electrons in a Circuit

It is not the electrons that move at this speed. It is the electric field that can travel through a circuit at nearly the speed of light.

Rate of electric flow

Measured in ampere (1 coulomb of charge per second).

Flow of charged particles In fluids

Positive ions and electrons constitute electric charge flow.

Electric power

Rate at which electric energy is converted into another form In equation form: Power = current voltage In units: watts

Semiconductors

Refers to materials that can alternate between being conductors and insulators Example: Germanium Silicon Zinc oxide

Ohm's law

Relationship between voltage, current, and resistance States that the current in a circuit varies in direct proportion to the potential difference, or voltage, and inversely with the resistance

Converting from ac to dc

When input to a diode is ac, output is pulsating dc. Slow charging and discharging of a capacitor provides continuous and smoother current. A pair of diodes is used, so there are no gaps in current output. The pair of diodes reverses the polarity of alternate half-cycles instead of eliminating them.

Electric potential difference In chemical batteries

Work by chemical disintegration of zinc or lead in acid. Energy stored in chemical bonds is converted to electric potential energy.

diode

a tiny electronic device that acts as a one-way valve to allow electron flow in one direction only.

potential difference

charge flows from one end to the other. Analogous to water flowing from higher pressure to lower pressure

Resistors

circuit elements that regulate current inside electrical devices

When you double the voltage in a simple electric circuit, you double the current. resistance. Both A and B. Neither A nor B.

current.

series

forms a single pathway for electron flow between the terminals of the battery, generator, or wall outlet

parallel

forms branches, each of which is a separate path for the flow of electrons

A continuous flow

is possible if the difference in water levels—hence the difference in water pressures—is maintained with the use of a pump.

When two identical lamps in a circuit are connected in parallel, the total resistance is less than the resistance of either lamp. the same as the resistance of each lamp. more than the resistance of each lamp. None of the above.

less than the resistance of either lamp. Resistors in parallel are like extra lines at a checkout counter. More lines means less resistance, allowing for more flow.

Consider a lamp powered by a battery. Charge flows out of the battery and into the lamp. from the negative terminal to the positive terminal. with a slight time delay after closing the switch. through both the battery and the lamp.

through both the battery and the lamp. Explanation: Remember, charge is already in all parts of the conducting circuit. The battery simply gets the charges moving. As much charge flows in the battery as outside. Therefore, charge flows through the entire circuit.

Current in a circuit is dependent on

voltage. electrical resistance in ohms.