11.3 Electrical Potential Difference p

The Battery To understand fully how circuits work, we need to take a closer look at the role of the battery. Current does not move by itself — there must be a battery that forces the electrons through the circuit and provides energy to the components. As the charges pass through a battery, it increases their potential energy.

Analogy – Water Pump

The pump increases the potential energy of water by lifting it to a certain height. The potential energy of the water depends on the mass of the water and the height to which it is lifted. Therefore it is useful to define a reference point where the potential energy is zero, which is at the bottom of the pump. The maximum potential energy is at the top of the pump. For electrical potential energy we will take the negative terminal of the battery as the point of zero potential energy.

Electrical Potential In an electrical circuit, it is not practical to refer to the potential energy of the charges as they move through the circuit. This is because potential energy depends on the quantity of charge, which changes as the circuit operates. It is more practical to use a measurement that is independent of the amount of charge flowing in the circuit.

electrical potential - the amount of electrical potential energy per unit charge. Electrical potential is represented by the symbol V, and its units are volts (V). It can be written mathematically as: where V is the electrical potential in volts (V), E is the electrical potential energy in joules (J), and q is the charge in coulombs (C). Note that the electrical potential is the same whether there are many charges (large current) or few charges (small current) flowing through the circuit.

Potential Difference As charges pass through a load in the circuit, they transfer energy to the load. The charges have a greater electrical potential before they pass through the load than after they pass through the load. This change in potential is referred to as the potential difference (ΔV). Potential difference is measured in volts (V). Potential difference is also referred to as voltage. The potential difference is always measured between two points in the circuit

A load within a circuit uses energy and decreases the potential. This creates a negative potential difference, which is also called a voltage drop, across the component. A voltage drop implies a loss of energy so a negative sign is not usually used. The combination of all the voltage drops in a circuit will decrease the potential by exactly the same amount as the battery increases the potential.

What is electric potential? portal.com/academy/lesson/electric-potential- charge-collections-and-volt-unit.html portal.com/academy/lesson/electric-potential- charge-collections-and-volt-unit.html portal.com/academy/lesson/electric-potential- charge-collections-and-volt-unit.html portal.com/academy/lesson/electric-potential- charge-collections-and-volt-unit.html rg rg rg rg

Measuring Potential Difference To measure potential difference, we use a voltmeter. The voltmeter must be placed across two points in the circuit and it will measure the voltage drop across that portion of the circuit (in parallel)

Sample problem A potential difference of 10.0 V is measured across a resistor in a circuit. If a charge of 20.0 C passes through the resistor, how much electrical energy is dissipated as heat?

Section 11.3 Sources, Loads, Gains, and Drops Fill in the blanks using the given terms. voltage __________ at __________ load drop gain source

Section 11.3 Sources, Loads, Gains, and Drops Fill in the blanks using the given terms. voltage __________ at __________ load drop gain source gain drop source load

Why are the readings on the two voltmeters the same? What does this suggest about the loss of voltage in the wires of the circuit? Section 11.3 Discussion: Sources, Loads, Gains, and Drops

Answers for Discussion Questions: The two readings are the same because the light is the only load in the circuit, so the voltage gain at the source exactly balances the voltage drop at the load. This suggests that there is no significant loss of voltage in the rest of the circuit. Section 11.3

Homework P. 511 practice #1 P. 511 practice #1 P. 513 questions #1-4,8 P. 513 questions #1-4,8

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