P#Y$1(S: Blog 1: Current Electricity and Electric Circuits

Sept 8, 2010
Pages 544-552

Here are my notes and thoughts regarding the chapter Current Electricity and Electric Circuits on pages 544 to 552.

-Electric current involves electrons repelling one another and passing through a conductor.

-The flow of charge is called electric current.

-The equation used to calculate current is the following:

I=Q/t

where I is the current in amperes (A), Q is the charge in coulombs (C), and t is the time in seconds

-An ammeter is a device that measures currents. It must be an excellent conductor because it cannot affect the amount of energy.

-In DC or direct current, the current flows in one direction. It starts from the power supply, goes through the conductor, and ultimately reaches the load.

-In AC or alternating current, the electrons constantly reverse their flow directions.

-In order for electric current to flow, it must have a complete path between the positive side and negative side. This path is called a circuit and it is essential for electric devices.

-The electrical potential energy for each coulomb of charge in a circuit is called the electric potential difference (V).

-The equation used to calculate electric potential difference is the following:

V=E/Q

E is the energy required to increase the electric potential of a charge, Q.

-Potential difference is often called voltage.

-The unit for potential difference is volt, named after Count Alessandro Volta.

-One volt (V) is the electric potential difference between two points if one joule of work (J) is required to move one coulomb (C) of charge between the points.

-The energy delivered to the load depends on the potential enrgy per charge and the rate at which the charge is delivered (current).

-To calculate the energy transferred by charge flow is the following:

E=VIt

where E in the energy in joules, V is the potential difference in volts, I is the current in amperes, and t is the time in seconds.

-Potential difference between any two points can be measured using a voltmeter.

Note: a voltmeter must be connected in parallel with a load in the circuit in order to compare the potential before and after the load.

-The voltmeter must have a large resistance-that is, it must be a much poorer conductor than the load to which it is connected, so that the measurement by the voltmeter will divert a minimal current from the circuit.