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Chapter 35 Electric Circuits Interpret circuit diagrams. Determine the equivalent resistance of circuits having two or more resistors. Explain the cause and prevention of overloading household circuits. Two Types of Circuits • 1. Series Circuit • 2. Parallel Circuit Series Circuit • In a series circuit, the current can only take one path. • All the current flows through every part of the circuit. – Christmas Lights – if you remove one bulb and the whole strand goes out, then they were made in series. Series Circuit Only one path to follow! Parallel Circuits • In parallel circuits, the current can take more than one path. –The electrical circuits in homes and buildings are parallel circuits Parallel Circuit MORE than one path to follow (THREE)! Ohm’s Law • Ohm’s Law states that the current of a circuit is the ratio of the voltage and the resistance of the circuit. •I=V/R – I = current (amps) – V = voltage (volts) – R = resistance (ohms) V I R 2009 Grade 10 Current • Current is the flow of electrical charges. • Current is measured in amperes. Resistance •Resistance (R) is a measure of how difficult it is for the charges to flow through the wire. Ohm’s Law • Ohm’s Law states that the current of a circuit is the ratio of the voltage and the resistance of the circuit. •I=V/R – I = current (amps) – V = voltage (volts) – R = resistance (ohms) V I R Practice Problem In this circuit, how much current flows through the light bulb? A B C D 0.75 amp 1.50 amps 2.0 amps 3.0 amps Current = voltage = V resistance R Current = 1.5 volts = 0.75 amp 2.0 ohms Voltage = Current x Resistance 9V = Amperes x 6 ohms or 9V/6ohms = • a. b. c. d. A 9 V battery is connected to a 6 Ohm resistor. How much current will flow through the circuit? 54 Amperes 15 Amperes 3 Amperes 1.5 Amperes 14 15 16 17 18 19 20 21 22 23 24 Home Which circuit is built so that if one lightbulb goes out, the other three lightbulbs will continue to glow? The other three bulbs will continue to glow. This is a parallel circuit. F, G, H above are series circuits. If this one goes out The Home others go out. If this one goes out 54 Home Home Which switch, if opened, will cause the light bulb to stop glowing? FQ GR HS JT If R was opened/off, If T was opened/off, the electricity would still go the electricity would still go through S to the bulb. through S to the bulb. If S was opened/off, the electricity would still go through R and T to the bulb. If Q was opened/off, Battery the electricity would NOT make it to the bulb. 32 Home How much current is flowing through this circuit? A 0.32 A B 3.1 A C 4.0 A D 12.5 A Current = 4 ÷ 12.5 47 What is the current in a copper wire that has a resistance of 2 Frequency = voltage ÷ resistance(ohms) ? = 9is ÷ 2connected ohms and to a 9-volt electrical source? Home Current (frequency) F 0.22 amp G 4.5 amps H 11.0 amps J 18.0 amps 46 Electricity travels in circuits • A circuit is a COMPLETE path through which electricity travels. • Example of a circuit is a toaster. • The handle pushed down connects the circuit. Parallel Circuits and Overloading • Lines carrying an unsafe load will be overload – To prevent overloading, fuses or circuit breakers are inserted in lines that provide power. Excessive current will “blow out” the fuse or “trip” the circuit breaker, stopping the current to prevent a short circuit. • Short circuits occur usually because of faulty wire insulation.