Current electricity Lesson 1: electric current

Current electricity Lesson 1: electric current
Lesson 2: Electrical Resistance Lesson 3: Ohm’s Law Lesson 4: Electrical Power Lesson 5: Circuit, Circuit Symbols and Circuit Connections Lesson 6: Series Circuits Lesson 7: Parallel Circuits

Lesson 1: Electric Current
The Electric Circuit and its Requirements Electric Current Common Misconceptions Regarding Electric Circuits

How to light a light bulb
Objective: light a light bulb Material: one battery, one wire, one light bulb. What you must do in order for the light bulb to work?

Light Bulb Anatomy A light bulb is a device consisting of a filament attached to two wires. The wires and the filament are conducting materials which allow charge to flow through them. One wire is connected to the ribbed sides of the light bulbs. The other wire is connected to the bottom base of the light bulb. The ribbed edge and the bottom base are separated by an insulating material which prevents the direct flow of charge between the bottom base and the ribbed edge. The only pathway by which charge can make it from the ribbed edge to the bottom base or vice versa is the pathway which includes the wires and the filament. +

What is an Electric Circuit?
A circuit is simply a closed loop through which charges can continuously move. The Requirement of a circuit There must be a closed conducting loop in the external circuit which stretches from the high potential, positive terminal to the low potential, negative terminal. There must be an energy supply capable doing work on charge to move it from a low energy location to a high energy location and thus establish an electric potential difference across the two ends of the external circuit.

Electric Current If the two requirements of an electric circuit are met, then charge will flow through the external circuit. This flow of charge or current, is the rate at which charge flows past a point on a circuit. Current is a rate quantity. Like velocity - the rate at which an object changes its position. Acceleration - the rate at which an object changes its velocity. And power - the rate at which work is done on an object. In every case of a rate quantity, the mathematical equation involves some quantity over time.

Definitions current: RATE OF CHARGE FLOW unit: C/s or AMPERE requires:
POTENTIAL DIFFERENCE PATH FOR FLOW

Example #1 100 coulombs of charge pass through point A in 4.0 seconds. What is the rate of current flow through point A? I = Δq / t I = 100 C / (4.00 s) I = 25 A A

Example #2 During a thunderstorm a lightning strike transfers 15.0 coulombs of charge in 10.0 milliseconds. What was the electrical current produced in the strike? I = Δq / t I = 15.0 C / (10 x 10-3 s) I = 1.5 x 105 A

Example #3 A wire carries a current of 50 amperes. I = Δq / t
How much charge flows through the wire in 10 seconds? How many electrons pass through the wire in 10 seconds? I = Δq / t 50 A = q / (10 s) q = 500 C 3.125 x 1021 e

example If charge flowing at the rate of 2.50 × 1016 elementary charges per second. What is the electric current?

Conventional Current Direction
The direction of an electric current is by convention the direction in which a positive charge would move.

Current versus Drift Speed
Current has to do with the number of coulombs of charge that pass a point in the circuit per unit of time. Drift speed refers to the average distance traveled by a charge carrier per unit of time. Even though the drift speed is extremely slow, the current could be big. This is because there are many, many charge carriers moving at once throughout the whole length of the circuit.

The Nature of Charge Flow
We know that the average drift speed of an electron is very, very slow, why does the light in a room or in a flashlight light immediately after the switched is turned on? Charge carriers in the wires of electric circuits are electrons. They are already there supplied by the atoms of the wire. Once the switch is turned to on, there is an electric potential difference established across the two ends of the external circuit. The electrons begin moving along a zigzag path in their usual direction. Thus, the flipping of the switch causes an immediate response throughout every part of the circuit, setting charge carriers everywhere in motion in the same net direction. While the actual motion of charge carriers occurs with a slow speed, the signal that informs them to start moving travels at a fraction of the speed of light.

Only energy can be used up, charge can never be used up
The charge carriers never become consumed or used up. While the energy possessed by the charge may be used up, the charge carriers themselves do not disintegrate, disappear or otherwise become removed from the circuit. And there is no place in the circuit where charge carriers begin to pile up or accumulate. The rate at which charge enters the external circuit on one end is the same as the rate at which charge exits the external circuit on the other end.

Lesson 2 - Electrical Resistance
Ohm's Law Power Revisited

LOW RESISTIVITY, SHORT, WIDE, COLD
Definitions resistance: OPPOSITION TO CURRENT unit: Ω factors that change resistance: resistivity: MATERIAL length cross-sectional area temperature To build an “ideal” conductor with the smallest possible resistance you would select one that is: LOW RESISTIVITY, SHORT, WIDE, COLD L - the length of the wire (meters), A - the cross-sectional area of the wire (m2), ρ - the resistivity of the material (in Ω•meter). R - the resistance of the wire (in Ω)

Resistance Factors R ρ R A R L R Temp.

Example #1 Determine the resistance of a 1.0 meter long copper wire with a cross-sectional area of 0.01 meter2. R = ρL / A R = (1.72 x 10-8 Ω·m)(1.0 m) / (0.01 m2) R = 1.72 x 10-6 Ω

Example #2 A piece of wire that has a length of 5.0 x 107 meters and a cross-sectional area of meter2 has a resistance of 31.8 ohms. What is the composition of this wire? R = ρL / A ρ = RA / L ρ = (31.8 Ω)(0.025 m2) / (5.0 x 107 m) ρ = 1.59 x 10-8 Ω·m

example An incandescent light bulb is supplied with a constant potential difference of 120 volts. As the filament of the bulb heats up, What happens to the resistance? What happens to the current?

example If the cross-sectional area of a metallic conductor is halved and the length of the conductor is doubled, the resistance of the conductor will be ______________. halved doubled unchanged quadrupled

example A 12.0-meter length of copper wire has a resistance of 1.50 ohms. How long must an aluminum wire with the same cross-sectional area be to have the same resistance?

example Pieces of aluminum, copper, gold, and silver wire each have the same length and the same cross-sectional area. Which wire has the lowest resistance at 20°C?

Lesson 3 – Ohm’s Law Know: Understand Be able to
Equation for Ohm’s Law. Understand Current is directly proportional to voltage and inversely proportional to electrical resistance. Be able to Determine current; voltage; resistance; and/or power in a system with a single resistor. Sketch/interpret graphs of relating voltage; current; resistance; Determine whether or not a particular object obeys Ohm’s Law.

Ohm’s Law Voltage results in current flow More voltage = more current
Resistance opposes current flow More resistance = less current

Resistance: R = V / I R is the slope of a potential difference vs. current graph. The resistance is a constant for a metallic conductor at constant temperature. V V Slope is resistance I I Non-Ohmic material Ohmic material

Graphs: I vs. V and I vs. R I I V I vs. V I vs. R
Current and potential difference have a direct relationship. The slope is equivalent to the reciprocal of the resistance of the resistor. Current and resistance have an inverse relationship

Ohm's Law as a Predictor of Current
The current in a circuit is directly proportional to the electric potential difference impressed across its ends and inversely proportional to the total resistance offered by the external circuit. The greater the battery voltage (i.e., electric potential difference), the greater the current. a twofold increase in the battery voltage would lead to a twofold increase in the current (if all other factors are kept equal). The greater the resistance, the less the current. An increase in the resistance of the load by a factor of two would cause the current to decrease by a factor of two to one-half its original value.

Check Your Understanding
Which of the following will cause the current through an electrical circuit to decrease? Choose all that apply. a. decrease the voltage b. decrease the resistance c. increase the voltage d. increase the resistance

A copper wire is connected across a constant voltage source. The current flowing in the wire can be increased by increasing the wire's cross-sectional area length resistance temperature

A series circuit has a total resistance of 1.00 × 102 ohms and an applied potential difference of 2.00 × 102 volts. What is the amount of charge passing any point in the circuit in 2.00 seconds?

A long copper wire was connected to a voltage source. The voltage was varied and the current through the wire measured, while temperature was held constant. Using the graph to find the resistance of the copper wire.

A student conducted an experiment to determine the resistance of a light bulb. As she applied various potential differences to the bulb, she recorded the voltages and corresponding currents and constructed the graph below. The student concluded that the resistance of the light bulb was not constant. What evidence from the graph supports the student’s conclusion? According to the graph, as the potential difference increased, what happens to the resistance of the light bulb?

A circuit consists of a resistor and a battery. Increasing the voltage of the battery while keeping the temperature of the circuit constant would result in an increase in current, only resistance, only both current and resistance neither current nor resistance

Sketch a graph that best represents the relationship between the potential difference across a metallic conductor and the electric current through the conductor At constant temperature T1 At a higher constant temperature T2. V I

A 1.5-volt, AAA cell supplies 750 milliamperes of current through a flashlight bulb for 5.0 minutes, while a 1.5-volt, C cell supplies 750 milliamperes of current through the same flashlight bulb for 20. minutes. Compared to the total charge transferred by the AAA cell through the bulb, the total charge transferred by the C cell through the bulb is half as great twice as great the same four times as great

Example #1 A potential difference of 25.0 volts is supplied to a circuit with 100 ohms of resistance. How much current flows through this circuit? I = V / R I = 25.0 V / 100 Ω I = 0.25 A

Example #2 A current of 2.0 amperes flows through a 10 ohm resistance.
What voltage must be applied to this resistance? I = V / R V = IR V = (2.0 A)(10 Ω) V = 20 V

Example #3 A 10 volt battery establishes a current of 5.0 amperes in a circuit. What is the resistance of this circuit? I = V / R R = V / I R = (10 A) / (5.0 A) R = 2.0 Ω

Lesson 4: Electrical Power
Know: Definition and equation for electrical power. Understand Power is directly proportional to both voltage and current. Be able to Determine power in a system with a single resistor. Sketch/interpret graphs of relating voltage; current; resistance and power with each other (assuming that all other variables are fixed.)

Power: Putting Charges to Work
Electrical devices, generally referred to as loads, have power ratings. A 1200 W hair dryer indicates it transfers 1200 Joules of electrical energy to heat, wind, sound energy in 1 second. The unit of power is watt. 1 watt = 1 joule / second A circuit with a battery and a wire leading from positive to negative terminal without a load would lead to a high rate of charge flow. Such a circuit is referred to as a short circuit. It would heat the wires to a high temperature and drain the battery of its energy rather quickly.

Power Law Moving electrons (current) requires ENERGY
How much energy gets used depends on: Strength of push – VOLTAGE Rate of flow – CURRENT

Example #1 A 12 volt battery is connected to a circuit which allows 10 amperes of current to flow. What is the power output of this circuit? P = IV P = (12 V)(10 A) P = 120 W

Example #2 A 100 watt light bulb is connected to a 120 volt power supply. What amount of current must pass through the light bulb? P = IV 100 W = (120 V) I I = A

Example #3 A 2.0 ampere current passes through a circuit with a 300 ohm resistance. What is the power generated in this circuit? P = I2 R P = (2.0 A)2 (300 Ω) P = 1200 W or 1.2 kW

Different units for power
P = I2•R relate current and resistance to power, notice double importance of current. Unit: A2∙Ω P = V2/R relate potential difference and resistance to power, notice double importance of potential difference. Unit: V2/Ω P = V·I relate potential difference and current to power. Notice that both have equal importance. Unit: V∙A Warning: While these three equations provide one with convenient formulas for calculating unknown quantities in physics problems, one must be careful to not misuse them by ignoring conceptual principles regarding circuits.

Check your understanding
If a 60-watt bulb in a household lamp was replaced with a 120-watt bulb, then how many times greater would the current be in that lamp circuit?

Which is a unit of electrical power? volt/ampere ampere/ohm ampere2/ohm volt2/ohm

Graphs of power vs. R, I, V P = VI = I2R = V2/R
When V is constant: P = VI; P = V2/R – common house hold appliances When R is constant: P = I2R; P = V2/R – same appliances P P Inverse, high R, low P V is slope R I P P Direct squared Direct squared I V

As the resistance of a constant-voltage circuit is increased, the power developed in the circuit decreases increases remains the same

The potential difference applied to a circuit element remains constant as the resistance of the element is varied. Graph power (P) vs. resistance (R) for this circuit. P R

Graph the relationship between the electrical power and the current in a resistor that obeys Ohm’s Law. P I

An electric motor uses 15 amperes of current in a 440-volt circuit to raise an elevator weighing 11,000 Newtons. What is the average speed attained by the elevator?

example To increase the brightness of a desk lamp, a student replaces a 60-watt light bulb with a 100-watt bulb. Compared to the 60-watt bulb, the 100-watt bulb has less resistance and draws more current less resistance and draws less current more resistance and draws more current more resistance and draws less current

Which would be thicker (wider) - the filament of a 60-Watt light bulb or the filament of a 100-W light bulb? Explain. Calculate the resistance and the current of a 7.5-Watt night light bulb plugged into a US household outlet (120 V).

Electrical energy E = P∙t = V∙I∙t = I2∙R∙t = (V2/R)∙t
The SI unit for energy is Joule. 1 joule = (1 Newton)(1 meter) = (1 kg∙m/s2)(1 meter) = 1 kg∙m2/s2

The kilowatt-hour Electrical utility companies provide energy for homes charge those homes for the electrical energy they used. A typical bill will contain a charge for the number of kilowatt-hours of electricity which were consumed. How many Joules is in one kWh?

Your 60-watt light bulb is plugged into a 110-volt household outlet and left on for 10 hours. The utility company charges you $0.20 per kWh. What is the cost? A current of 0.40 ampere is measured in a 150 ohm resistor, how much energy is expended by the resistor in 20. seconds? An electric dryer consumes 6.0 × 106 joules of energy when operating at 220 volts for 30. minutes. During operation, how much current does the dryer draws approximately?

Energy can be transformed, but is conserved
The purpose of every circuit is to supply the energy to operate various electrical devices. These devices are constructed to convert the energy of flowing charge into other forms of energy (e.g., light, thermal, sound, mechanical, etc.). Use complete sentences to describe the energy conversions that occur in the following devices. Windshield wipers on a car Defrosting circuit on a car Hair dryer

Rechargeable Batteries
Rechargeable batteries has nothing to do with charges. Rechargeable batteries rely upon a reversible reaction, turning the chemical products back into chemical reactants within the cell.

Alert: Statement True or False?
When an electrochemical cell no longer works, it is out of charge and must be recharged before it can be used again. An electrochemical cell can be a source of charge in a circuit. The charge which flows through the circuit originates in the cell. Charge becomes used up as it flows through a circuit. The amount of charge which exits a light bulb is less than the amount which enters the light bulb. Charge flows through circuits at very high speeds. This explains why the light bulb turns on immediately after the wall switch is flipped. The local electrical utility company supplies millions and millions of electrons to our homes everyday.

Example A 12.0-meter length of copper wire has a resistance of 1.50 ohms. How long must an aluminum wire with the same cross-sectional area be to have the same resistance?

Example Calculate the resistance of a 1.00-kilometer length of nichrome wire with a cross-sectional area of 3.50 × 10-6 meter2 at 20°C.

The tendency to give attention to units is an essential trait of any good physics student.
Many of the difficulties associated with solving problems may be traced back to the failure to give attention to units. As more and more electrical quantities and their respective metric units are introduced, it will become increasingly important to organize the information in your head.

Quantities, Symbols, Equations and Units!
Quantity Symbol Equations Standard Metric Unit Other Units Potential Difference (a.k.a. voltage) V V= W / Q V = I • R Volt (V) J / C Current I I = Q / t I = V / R Amperes (A) C / s V / Ω Power P P = W / t P = V∙I P = V2/R P = I2R Watt (W) J / s V∙A V/ Ω2 A2∙Ω Resistance R R = ρ•L / A R = V / I Ohm (Ω ) V / A Energy W W = V • Q W = P • t Joule (J) V • C W • s

Lesson 5: Circuit, Circuit Symbols and Circuit Connections
What is a circuit? Circuit Symbols and Circuit Diagrams Two Types of Connections

What is a circuit? A continuous loop through which current flows from an area of high voltage to a an area of low voltage.

Circuit Symbols Voltage sources Resistances Other Elements
Measurement Devices

Circuit Elements – Measuring Devices
Measures: VOLTAGE Resistance: HIGH Connect to circuit: OUTSIDE Measures CURRENT Resistance: LOW Connect to circuit: INSIDE voltmeter ammeter

Potential differences
Meters in a Circuit V 5V R = 2.5Ω 2A 2A V V A 0V A 0V Voltmeter measures RELATIVE Potential differences from OUTSIDE the circuit Ammeter measures Current flow INSIDE the circuit V = 5V V 5V

Meters in a circuit V A V A

Two types of connections
Three D-cells are placed in a battery pack to power a circuit containing three light bulbs Schematic Diagram of Circuit Only use circuit symbols in your reference table to draw the circuits Schematic Diagram of Circuit

Series and Parallel connections
These two examples illustrate the two common types of connections made in electric circuits. When two or more resistors are present in a circuit, they can be connected in series or in parallel.

For series circuits As more resistors are added the overall current within the circuit decreases. This decrease in current is consistent with the conclusion that the overall resistance increases. If one of three bulbs in a series circuit is unscrewed from its socket, then the other bulbs immediately go out.

For parallel circuits As the number of resistors increases, the overall current also increases. This increase in current is consistent with a decrease in overall resistance. Adding more resistors in a separate branch has the unexpected result of decreasing the overall resistance! If an individual bulb in a parallel branch is unscrewed from its socket, other bulbs are not effected.

1. Observe the electrical wiring below. Indicate whether the connections are series or parallel connections. Explain each choice.

2. Two electric circuits are diagrammed below
2. Two electric circuits are diagrammed below. For each circuit, indicate which two devices are connected in series and which two devices are connected in parallel. In series? ______________ In parallel? ______________ In series ________________

Lesson 6 Series Circuits
Be able to Sketch diagrams of series circuits including proper placement of meters. VIR charts and Ohm’s Law to solve series circuits problems. Determine the power or electrical energy used by a circuit component or an entire circuit. Determine the effect of adding or removing resistors to the rest of a circuit.

Definitions series circuit – a circuit in which two or more elements are connected end-to-end so that a single loop of current is formed. Same current flows through the all resistor. The potential difference of across the bigger resistor is higher than the potential difference across the smaller resistor. By the time each charge makes it back to the battery, it has lost all the electrical energy given to it by the battery.

Series Circuit Rules equivalent Resistance – more resistors = more resistance RT = R1 + R2 + … current – same throughout circuit IT = I1 = I2 = … voltage – voltages add up VT = V1 + V2 + … All circuit components and the circuit as a whole must obey Ohm’s Law Req is same as RT Ieq is same as IT Veq is same as VT

V (V) I (A) R (Ω) R1 R2 R3 Req 5.0 Ω 8.0 Ω 2.0 Ω R1 R2 R3 7.5 V 2.5
0.5 5.0 4.0 0.5 8.0 1.0 0.5 2.0 7.5 0.5 15

V (V) I (A) R (Ω) R1 R2 R3 Req 50 Ω 120 Ω 150 Ω R1 R2 R3 1.5A 75 1.5
180 1.5 120 225 1.5 150 480 1.5 320

Example A series circuit has a total resistance of 1.00 x 102 ohms and an applied potential difference of 2.00 x 102 volts. What is the amount of charge passing any point in the circuit in 2.00 seconds? I = V / R = 2.00 x 102 V / 1.00 x 102 Ω I = 2.00 A I = Q / t 2.00 A = Q / 2.00 s Q = 4.00 C

Lesson 7 Parallel Circuits
Be able to Sketch diagrams of parallel circuits including proper placement of meters. VIR charts and Ohm’s Law to solve parallel circuits problems. Determine the power or electrical energy used by a circuit component or an entire circuit. Determine the effect of adding or removing resistors to the rest of a circuit.

Definitions parallel circuit – a circuit in which two or more elements are connected so that each has its own current loop. More current flows through the smaller resistor. (More charges take the easiest path.) The potential difference of different resistors are the same, they all have the same drop. By the time each charge makes it back to the battery, it has lost all the electrical energy given to it by the battery.

Parallel Circuit Rules
equivalent Resistance – more resistors = less resistance 1/Req = 1/R1 + 1/R2 + … current – currents add up I = I1 + I2 + … voltage – voltages same for each resistor V = V1 = V2 = … All circuit components and the circuit as a whole must obey Ohm’s Law

Current In a parallel circuit, charge divides up into separate branches such that there can be more current in one branch than there is in another. Nonetheless, when taken as a whole, the total amount of current in all the branches when added together is the same as the amount of current at locations outside the branches. Itotal = I1 + I2 + I

Junction Rule The total current flowing into and out of a junction must be the same 10 A 6.0 A ? 4.0 A

Junction Rule 6.0 A 10 A 6.0 A ? ? 4.0 A 2.0 A

Example The diagram shows the current in three of the branches of a direct current electric circuit. The current in the fourth branch, between junction P and point W, must be 1 A toward point W 1 A toward point P 7 A toward point W 7 A toward point P

Example The diagram shows a current in a segment of a direct current circuit. What is the reading of ammeter A?

Equivalent Resistance
The equivalent resistance (total resistance) of a circuit is the amount of resistance which a single resistor would need in order to equal the overall effect of the collection of resistors which are present in the circuit. For parallel circuits, the mathematical formula for computing the equivalent resistance (Req) is where R1, R2, and R3 are the resistance values of the individual resistors which are connected in parallel.

For parallel circuit, adding more resistors you add the less resistance you have.

Example – determine equivalent R
Regents Physics - Current Electricity Notes Example – determine equivalent R Note: the equivalent resistance is less than any single resistance in the circuit.

Example Resistors R1 and R2 have an equivalent resistance of 6 ohms when connected as shown. What is the resistance of R1? 3 ohms 4 ohms 5 ohms 8 ohms Since the equivalent resistance is smaller than any single resistance in the parallel circuit, the answer is 8 ohms

Example Resistors R1 and R2 have the same resistance. When they are connected together as shown, they have an equivalent resistance of 4 ohms. What is the resistance of R1? Since R1 = R2 1/4 Ω = 1/R1 + 1/R1 = 2/R1 R1 = 8 Ω Note: the individual resistance is bigger than the total resistance in the parallel circuit.

Voltage Drops for Parallel Branches
The total voltage drop in the external circuit is equal to the gain in voltage as a charge passes through the internal circuit. In a parallel circuit, a charge does not pass through every resistor; rather, it passes through a single resistor. Thus, the entire voltage drop across that resistor must match the battery voltage. It matters not whether the charge passes through resistor 1, resistor 2, or resistor 3, the voltage drop across the resistor which it chooses to pass through must equal the voltage of the battery. Put in equation form, this principle would be expressed as Vbattery = V1 = V2 = V3 = ..

All COMPONENTS and the WHOLE CIRCUIT obey Ohm’s Law
I1 = V / R1 I2 = V / R2 I3 = V / R3

V (V) I (A) R (Ω) R1 R2 R3 Req R3 = 30 Ω R2 = 30 Ω R1 = 30 Ω 60 V 60
2.0 30 60 2.0 30 60 2.0 30 60 6.0 10

V (V) I (A) R (Ω) R1 R2 R3 Req R3 = 10 Ω R2 = 50 Ω R1 = 20 Ω 0.5 A 5.0
0.25 20 5.0 0.1 50 5.0 0.5 10 5.0 0.85 5.9

Example In the diagram, what is the potential difference across the 3.0-ohm resistor?

Example Circuit A and circuit B are shown in the diagram. Compared to the total resistance of circuit A, the total resistance of circuit B is less greater the same

Example In the diagram of a parallel circuit, ammeter A measures the current supplied by the 110-volt source. What is the current measured by ammeter A? 11 A

Example Two resistors are connected to a source of voltage as shown in the diagram. At which position should an ammeter be placed to measure the current passing only through resistor R1? position 1 position 2 position 3 position 4

Example Three ammeters are placed in a circuit as shown in the diagram. If A1 reads 5.0 amperes and A2 reads 2.0 amperes, what does A3 read? 3 A

Example In the circuit shown in the diagram, which is the correct reading for meter V2?

Example Which circuit could be used to determine the total current and potential difference of a parallel circuit? A B C D

Example In the circuit shown in the diagram, what is the potential difference of the source?

Example Which circuit below would have the lowest voltmeter reading? A

Example In which pair of circuits shown in the diagram could the readings of voltmeters V1 and V2 and ammeter A be correct? A and B B and C C and D A and D

Example Which statement about ammeters and voltmeters is correct?
The internal resistance of both meters should be low. Both meters should have a negligible effect on the circuit being measured. The potential drop across both meters should be made as large as possible. The scale range on both meters must be the same.

Example In the diagram below, lamps L1 and L2 are connected to a constant voltage power supply. If lamp L1 burns out, What will happen to the equivalent resistance of the circuit? What will happen to the total current of the circuit? What will happen to the brightness of L2 ?

Example Identical resistors (R) are connected across the same 12-volt battery. Which circuit uses the greatest power? A B C D

Lab 15 – Resistance PURPOSE:
Determine the relationship between Resistance and the length of the wire Determine the relationship between Resistance and the area of the wire Determine resistivity of the wire MATERIAL: Nichrome wire boards, multipurpose meter, ruler, graph paper DATA: diameter _________ m Area __________m2 Length _________ m Length (m) Resistance ∙Area (Ω∙m2) R (Ω) L (m) R (Ω) Area (m2)

Current electricity Lesson 1: electric current

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