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Resisting the Movement of Charge. When we want to slow down the flow of a charge, we add a resistor to the circuit. . Resistance is a property of a substance that hinders motion of electric energy into other forms of energy.
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Resisting the Movement of Charge • When we want to slow down the flow of a charge, we add a resistor to the circuit.
Resistance is a property of a substance that hinders motion of electric energy into other forms of energy.
For example, resistors in light bulbs slow down charge and convert electricity to light and heat.
How are Voltage, Current, and Resistance Related? • Current is the movement of electrons. • Voltage is the energy that makes electrons move. • Resistance is what opposes the motion of electrons.
Conductors = poor resistors. • Insulators = good resistors.
Variable Resistors • Do not have a fixed resistance. • Resistance can change due to temperature, light, or voltage. • Variable resistors are used in light dimmers, thermostats, and motor speed controls.
Calculating Resistance • Resistance is measured in ohms, (Ω). • Resistance is measured with an ohmmeter.
Ohm’s Law Resistance (R) = Voltage (V) Current (I)
The current remains constant throughout the circuit. • The brightness of each bulb will decrease throughout the circuit. • If a bulb is removed, the circuit will not work.
The total current is divided through each branch. • The brightness of each bulb will remain the same.
Household Wiring • Homes are wired with parallel circuits. • This allows two appliances to be on at the same time without reducing power available to each.
However, if too many appliances are turned on at the same time, a fire may begin. • To prevent this, fuses or circuit breakers are used.
Voltage Calculations in Series and Parallel Circuits • Review: • Series Circuit: One continuous path connected as a loop. • Parallel Circuit: Have several paths, or branches in which current can flow.
In a series circuit, each cell provides energy to the circuit. Example: Each battery has 1.5V. What is the total voltage of 1 battery, 2 batteries, and 3 batteries in a series circuit? 1 battery = 1.5 V 2 batteries = 1.5 + 1.5 = 3.0 V 3 batteries = 1.5 + 1.5 + 1.5 = 4.5V
In a parallel circuit, each cell works by itself. Example: Each battery has 1.5V. What is the total voltage of 1 battery, 2 batteries, and 3 batteries, in a parallel circuit? 1 battery = 1.5V 2 batteries = 1.5V 3 batteries = 1.5V
Practice Questions 1) What is the voltage of two 4.5 volt batteries connected in series? 2) What is the voltage of two 2.3 volt batteries connected in parallel? 3) How does the voltage of six 1.5 volt batteries connected in parallel compare to six 1.5 volt batteries connected in series?