Slide 26 / 105 9 What is the current in a wire whose resistance is 3 # if 1.5 V is applied to it? https://www.njctl.org/video/?v=n2z73ToNdrQ
Slide 26 (Answer) / 105 9 What is the current in a wire whose resistance is 3 # if 1.5 V is applied to it? Answer [This object is a pull tab] https://www.njctl.org/video/?v=n2z73ToNdrQ
Slide 27 / 105 10How much voltage is needed in order to produce a 0.70 A current through a 490 # resistor? https://www.njctl.org/video/?v=WXSW7nHi2XY
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Slide 28 / 105 11 How much voltage is needed in order to produce a 0.5 A current through a 150 # resistor? https://www.njctl.org/video/?v=uhg76Swygls
Slide 28 (Answer) / 105 11 How much voltage is needed in order to produce a 0.5 A current through a 150 # resistor? Answer [This object is a pull tab] https://www.njctl.org/video/?v=uhg76Swygls
Slide 29 / 105 12 What is the resistance of a rheostat coil, if 0.05 A of current flows through it when 6 V is applied across it? https://www.njctl.org/video/?v=rqsfe8lEoTk
Slide 29 (Answer) / 105 12 What is the resistance of a rheostat coil, if 0.05 A of current flows through it when 6 V is applied across it? Answer [This object is a pull tab] https://www.njctl.org/video/?v=rqsfe8lEoTk
Slide 30 / 105 13 What is the resistance of a rheostat coil, if 20 A of current flows through it when 1000 V is applied across it? https://www.njctl.org/video/?v=YQCfqYSBs0k
Slide 30 (Answer) / 105 13 What is the resistance of a rheostat coil, if 20 A of current flows through it when 1000 V is applied across it? Answer [This object is a pull tab] https://www.njctl.org/video/?v=YQCfqYSBs0k
Slide 31 / 105 Electrical Power P = W Power is defined as work per unit time t P = QV if W = QV then substitute: t if then substitute: I = Q P = IV t What happens if the current is increased? What happens if the voltage is decreased? https://www.njctl.org/video/?v=Cm8VmJSk5iY
Slide 32 / 105 Electrical Power Let's think about this another way... The water at the top has GPE & KE. As the water falls, it loses GPE and the wheel gets turned, doing work.When the water falls to the bottom it is now slower, having done work.
Slide 33 / 105 Electrical Power Electric circuits are similar. A charge falls from high voltage to low voltage. In the process of falling energy may be used (light bulb, run a motor, etc). What is the unit of Power?
Slide 34 / 105 Electrical Power How can we re-write electrical power by using Ohm's Law? (electrical power) (Ohm's Law) I = V P = IV R P = VV R P = V 2 R
Slide 35 / 105 Electrical Power Is there yet another way to rewrite this? I = V can be rewritten as V = IR. R (electrical power) (Ohm's Law) V = I R P = IV We can substitute this into Power P = I(IR) P = I 2 R
Slide 36 / 105 Batteries D, C, AA, & AAA have the same voltage, however they differ in the amount of power they deliver. For instance, D 9 V batteries can deliver D more current and AAA AA C therefore more power. 1.5 V
Slide 37 / 105 14 A toy car's electric motor has a resistance of 17 # ; find the power delivered to it by a 6-V battery. https://www.njctl.org/video/?v=zGPEnMSjQH0
Slide 37 (Answer) / 105 14 A toy car's electric motor has a resistance of 17 # ; find the power delivered to it by a 6-V battery. Answer [This object is a pull tab] https://www.njctl.org/video/?v=zGPEnMSjQH0
Slide 38 / 105 15 A toy car's electric motor has a resistance of 6 # ; find the power delivered to it by a 7-V battery. https://www.njctl.org/video/?v=7HCqGr-Kr4Q
Slide 38 (Answer) / 105 15 A toy car's electric motor has a resistance of 6 # ; find the power delivered to it by a 7-V battery. Answer [This object is a pull tab] https://www.njctl.org/video/?v=7HCqGr-Kr4Q
Slide 39 / 105 16 What is the power consumption of a flash light bulb that draws a current of 0.28 A when connected to a 6 V battery? https://www.njctl.org/video/?v=H3gFobVzbU8
Slide 39 (Answer) / 105 16 What is the power consumption of a flash light bulb that draws a current of 0.28 A when connected to a 6 V battery? Answer [This object is a pull tab] https://www.njctl.org/video/?v=H3gFobVzbU8
Slide 40 / 105 17 What is the power consumption of a flash light bulb that draws a current of 0.33 A when connected to a 100 V battery? https://www.njctl.org/video/?v=cFhbxaJnBMc
Slide 40 (Answer) / 105 17 What is the power consumption of a flash light bulb that draws a current of 0.33 A when connected to a 100 V battery? Answer [This object is a pull tab] https://www.njctl.org/video/?v=cFhbxaJnBMc
Slide 41 / 105 18 A 30Ω toaster consumes 560 W of power: how much current is flowing through the toaster? https://www.njctl.org/video/?v=aYfmw00jqXk
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Slide 42 / 105 19 A 50Ω toaster consumes 200 W of power: how much current is flowing through the toaster? https://www.njctl.org/video/?v=JK0j3faqvjc
Slide 42 (Answer) / 105 19 A 50Ω toaster consumes 200 W of power: how much current is flowing through the toaster? Answer [This object is a pull tab] https://www.njctl.org/video/?v=JK0j3faqvjc
Slide 43 / 105 20 When 30 V is applied across a resistor it generates 600 W of heat: what is the magnitude of its resistance? https://www.njctl.org/video/?v=qss0lmcOMcM
Slide 43 (Answer) / 105 20 When 30 V is applied across a resistor it generates 600 W of heat: what is the magnitude of its resistance? Answer [This object is a pull tab] https://www.njctl.org/video/?v=qss0lmcOMcM
Slide 44 / 105 21 When 100 V is applied across a resistor it generates 200 W of heat: what is the magnitude of its resistance? https://www.njctl.org/video/?v=F5wMdXpRseM
Slide 44 (Answer) / 105 21 When 100 V is applied across a resistor it generates 200 W of heat: what is the magnitude of its resistance? Answer [This object is a pull tab] https://www.njctl.org/video/?v=F5wMdXpRseM
Slide 45 / 105 "Pipe" size How could the wire in the circuit affect the current? If wire is like a pipe, and current is like water that flows through the pipe... if there were pipes with water in them, what could we do to the pipes to change the speed of the water (the current)?
Slide 45 (Answer) / 105 "Pipe" size How could the wire in the circuit affect the current? If wire is like a pipe, and current is like water that flows through the pipe... change the cross-sectional area of the pipe making it bigger will allow more if there were pipes with water in Answer water to flow them, what could we do to the pipes to change the speed of the change the length of the pipe water (the current)? increasing the length will increase the time it takes for the water to get to the end of its trip [This object is a pull tab]
Slide 46 / 105 ** Resistivity and Resistance Return to Table of Contents https://www.njctl.org/video/?v=22iIFMgCbRk
Slide 47 / 105 Resistivity & Resisitance ** Every conductor "conducts" electric charge to a greater or lesser extent. The last example also applies to conductors like copper wire. Decreasing the length (L) or increasing the cross-sectional area (A) would increase conductivity. Also, the measure of a conductor's resistance to conduct is called its resistivity. Each material has a different resistivity. Resistivity is abbreviated using the Greek letter rho ( # ). Combining what we know about A, L, and ρ, we can find a conductor's total resistance. R = # L A
Slide 48 / 105 Resistivity & Resisitance ** R = # L A Resistance, R, is measured in Ohms (Ω). Ω is the Greek letter Omega. Cross-sectional area, A, is measured in m 2 Length, L, is measured in m Resistivity, ρ, is measured in Ωm How can we define A for a wire?
Slide 49 / 105 Resisitance ** # = RA L What is the resistance of a good conductor? Low; low resistance means that electric charges are free to move in a conductor. Click here for a PhET simulation about Resistance
Slide 50 / 105 ** Resistivities of Common Conductors Resistivity (10 -8 Ωm) Material Silver 1.59 Copper 1.68 Gold 2.44 Aluminum 2.65 Tungsten 5.60 Iron 9.71 Platinum 10.6 Mercury 98 Nichrome 100
Slide 51 / 105 22 Rank the following materials in order of best ** conductor to worst conductor. A Iron, Copper, Platinum B Platinum, Iron, Copper Resistivity (10 -8 Ωm) Material C Copper, Iron, Platinum Silver 1.59 Copper 1.68 Gold 2.44 Aluminum 2.65 Tungsten 5.60 Iron 9.71 Platinum 10.6 Mercury 98 Nichrome 100 https://www.njctl.org/video/?v=22iIFMgCbRk
Slide 51 (Answer) / 105 22 Rank the following materials in order of best ** conductor to worst conductor. A Iron, Copper, Platinum B Platinum, Iron, Copper Resistivity (10 -8 Ωm) Material C Copper, Iron, Platinum Silver 1.59 Copper 1.68 Gold 2.44 Aluminum 2.65 Tungsten 5.60 Answer Iron 9.71 C Platinum 10.6 Mercury 98 Nichrome 100 [This object is a pull tab] https://www.njctl.org/video/?v=22iIFMgCbRk
Slide 52 / 105 23 What is the resistance of a 2 m long copper wire ** whose cross-sectional area of 0.2 mm 2 ? https://www.njctl.org/video/?v=JzMdYb5U1a4
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Slide 53 / 105 24 An aluminum wire with a length of 900 m and a ** cross-sectional area of 10 mm 2 has a resistance of 2.5 # . What is the resistivity of the wire? https://www.njctl.org/video/?v=D6vB1-nTi-k
Slide 53 (Answer) / 105 24 An aluminum wire with a length of 900 m and a ** cross-sectional area of 10 mm 2 has a resistance of 2.5 # . What is the resistivity of the wire? Answer [This object is a pull tab] https://www.njctl.org/video/?v=D6vB1-nTi-k
Slide 54 / 105 25 What diameter of 100 m long copper wire would ** have a resistance of 0.10 # ? https://www.njctl.org/video/?v=O7fFFa3pQg4
Slide 54 (Answer) / 105 25 What diameter of 100 m long copper wire would ** have a resistance of 0.10 # ? Answer [This object is a pull tab] https://www.njctl.org/video/?v=O7fFFa3pQg4
Slide 55 / 105 26 What is the cross-sectional area of a 10Ω copper ** wire of length is 10000 meters? https://www.njctl.org/video/?v=xHiCi7u2RUI
Slide 55 (Answer) / 105 26 What is the cross-sectional area of a 10Ω copper ** wire of length is 10000 meters? Answer [This object is a pull tab] https://www.njctl.org/video/?v=xHiCi7u2RUI
Slide 56 / 105 27 What is the length of a 10 Ω copper wire whose ** diameter is 3.2 mm? https://www.njctl.org/video/?v=vpqKKgbpP-w
Slide 56 (Answer) / 105 27 What is the length of a 10 Ω copper wire whose ** diameter is 3.2 mm? Answer [This object is a pull tab] https://www.njctl.org/video/?v=vpqKKgbpP-w
Slide 57 / 105 Circuit Diagrams Return to Table of Contents https://www.njctl.org/video/?v=pW1a4hahYbE
Slide 58 / 105 Circuit Diagrams Drawing realistic pictures of circuits can be very difficult. For this reason, we have common symbols to represent each piece. Resistor Battery Wire *Note: Circuit diagrams do not show where each part is physically located.
Slide 59 / 105 Circuit Diagrams Draw a simple circuit that has a 9 V battery with a 3 Ω resistor across its terminals. What is the magnitude and direction of the current? Conventional current flows from the positive terminal to the negative terminal.
Slide 59 (Answer) / 105 Circuit Diagrams Draw a simple circuit that has a 9 V battery with a 3 Ω resistor across its terminals. What is the magnitude and direction of the current? R = 3 # Answer I = 3A I V = 9 V [This object is a pull tab] Conventional current flows from the positive terminal to the negative terminal.
Slide 60 / 105 Circuit Diagrams There are two ways to add a second resistor to the circuit. Series Parallel R 1 R 1 R 2 R 2 V V All charges must move Charges pass through through both resistors either R 1 or R 2 but not both. to get to the negative terminal.
Slide 61 / 105 Circuit Diagrams Are the following sets of resistors in series or parallel? R 1 R 1 V V R 2 R 2
Slide 61 (Answer) / 105 Circuit Diagrams Are the following sets of resistors in series or parallel? R 1 R 1 Answer V V R 2 R 2 Parallel Series The "test" is to trace the shortest route around the circuit. The resistors found on the same route are in series; those not found on the same route are in parallel to those that were. [This object is a pull tab]
Slide 62 / 105 Equivalent Resistance Resistors and voltage from batteries determine the current. Circuits can be redrawn as if there were only a single resistor and battery.By reducing the circuit this way, the circuit becomes easier to study. The process of reducing the resistors in a circuit is called finding the equivalent resistance (R eq ). R 1 R 2 V
Slide 63 / 105 Series Circuits: Equivalent Resistance R 1 R 2 What happens to the current in the circuit to the right? V
Slide 63 (Answer) / 105 Series Circuits: Equivalent Resistance R 1 R 2 What happens to the current in the circuit to the right? V Answer The current passing through all parts of a series circuit is the same. For example: I = I 1 = I 2 [This object is a pull tab]
Slide 64 / 105 Series Circuits: Equivalent Resistance R 1 R 2 What happens to the voltage as it moves around the circuit? V
Slide 64 (Answer) / 105 Series Circuits: Equivalent Resistance R 1 R 2 What happens to the voltage as it moves around the circuit? The sum of the voltage drops V across each of the resistors in a Answer series circuit equals the voltage of the battery. For example: V = V 1 + V 2 [This object is a pull tab]
Slide 65 / 105 Series Circuits: Equivalent Resistance If V = V 1 + V 2 + V 3 + ... substitute Ohm's Law solved for V is: V = IR IR = I 1 R 1 + I 2 R 2 + I 3 R 3 but since current (I) is the same everywhere in a series circuit, I = I 1 = I 2 = I 3 IR = IR 1 + IR 2 + IR 3 Now divide by I R eq = R 1 + R 2 + R 3 + ... To find the equivalent resistance (R eq ) of a series circuit, add the resistance of all the resistors.If you add more resistors to a series circuit, what happens to the resistance?
Slide 66 / 105 28 What is the equivalent resistance in this circuit? # R 2 = 3 R 1 = 5 # V = 9 V https://www.njctl.org/video/?v=t_KHxvQme3E
Slide 66 (Answer) / 105 28 What is the equivalent resistance in this circuit? # R 2 = 3 R 1 = 5 # Resistors in series: Answer V = 9 V [This object is a pull tab] https://www.njctl.org/video/?v=t_KHxvQme3E
Slide 67 / 105 29 What is the total current at any spot in the circuit? R 1 = 5 # R 2 = 3 # V = 9 V https://www.njctl.org/video/?v=E6vsTDb5_cw
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