Electricity

Can you get a light bulb to light? Using the equipment given to you, try to find as many ways as possible to get the light bulb to light. Diagram four ways in which you were able to get the light bulb to light. Label the battery, the wire, and the bulb. Diagram at least three ways in which you were not able to get the bulb to light. Questions: 1. From your observations, what conditions seem to be necessary in order for the bulb to light?

Successful Attempts

Producing Electric Current The flow of charged particles is an electric current. Charges flow from a conductor with a higher potential difference through a wire to a conductor with a lower potential difference. Conventional current is defined as positive charges flowing from the positive (high potential difference) plate to the negative (low potential difference) plate. The flow stops when the electric potential difference between the two plates is zero. If the charge particles are pumped back to the original conductor (plate) by an outside energy source (battery), the flow of charges will continue.

Electric Circuits Any closed loop or conducting path allowing electric charges to flow is called an electric circuit. A circuit includes a charge pump and a device that reduces the potential energy of the charges as they flow from one plate to another. The potential energy lost by the charges as they move through the connected device is usually converted to some other form of energy such as kinetic (motor), light (lamp), or thermal (heater).

Requirements that must be met to establish an electric current. There must be a closed conducting path that extends from the positive terminal to the negative terminal. It is not enough that there is simply a closed conducting loop; the loop itself must extend from the positive terminal to the negative terminal of the electrochemical cell.

Requirements (continued) The second requirement of an electric circuit that is common in each of the successful attempts is that there must be an electric potential difference across the two ends of the circuit. This is most commonly established by the use of an electrochemical cell, a pack of cells (i.e., a battery) or some other energy source.

In Summary In conclusion, there are two requirements that must be met in order to establish an electric circuit. The requirements are 1)There must be an energy supply capable of 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. 2)There must be a closed conducting loop in the external circuit that stretches from the high potential, positive terminal to the low potential, negative terminal.

When a battery no longer works, which requirement is not met? 10 An external energy supply to pump the charge The external circuit must make up a closed conducting loop Neither requirement is met. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

An external energy supply to pump the charge When a light bulb is burned out and no longer works, which requirement is not met? 10 An external energy supply to pump the charge The external circuit must make up a closed conducting loop Neither requirement is met. 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Electric Current Current is the rate at which charge flows past a point on a circuit. Current flows from the positive terminal to the negative terminal. Current (I) = q/t = Coulombs/sec=amperes (A) Example: A 2 mm long cross section of wire is isolated and 20 C of charge is determined to pass through it in 40 s. I = _____amperes Example: A 1 mm long cross section of wire is isolated and 2 C of charge is determined to pass through it in 0.5 s. I = ________amperes

Current is measured in units of ______. 10 Amperes Coulombs Volts Ohms 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

negative, positive positive, negative negative, negative The direction that conventional current flows in the external circuit is from the ___ terminal to the ____ terminal. 10 negative, positive positive, negative negative, negative positive, positive 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Electrons move very quickly through an electric circuit. 10 True False 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

If the current is measured as 6 A, then ____ C of charge flows past any point in the circuit in 3 s. 10 0.5 2 3 18 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Power Power (measured in watts, W) measures the rate at which energy is transferred. (1 W = 1J/s) The energy carried by an electric current depends on the charge transferred and the potential difference across which it moves. Current is the rate of charge flow (I=q/t). A flow of 1 C/s is called an ampere (A). Power is equal to the current times the potential difference. P = I V Total energy transferred = P x t (W.s or J)

Practice Problems A 6.0 V battery delivers a 0.50 A current to an electric motor connected across its terminals. What power is delivered to the motor? If the motor runs for 5.0 min, how much electric energy is delivered?

The Kilowatt- Hour The electric company (power company) provides energy rather than power. When a bill is paid, the customer is paying for the electric energy used. Because of the large amounts of energy consumed, electric companies measure sales in a units of kilowatt-hours. One kilowatt hour is equal to 1000 W being delivered for 3600 s (1 hr) or 3.6 x 106 J. How many 100 W light bulbs would have to be used for 1 full hour to consume 1 KWh of energy?

Practice Problem An electric heater draws 15.0 A from a 120 V source. It is operated, on the average, for 5.0 h each day. How much power does the heater use? How much energy in KWh does it consume in 30 days? At $0.12 per KWh, how much does it cost to operate the heater for 30 days?

Problem A TV has a power rating of 103 W. How much does it cost per month to operate it for 6 hours per weekday and 15 hours/day on the weekend? (Assume a 4 week month) How much current does it draw?

Power is measured in units called 10 amperes joules kilowatt-hours watts 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Current is measured in units called 10 amperes kilowatt-hours potential watts 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

If a 9.0 V battery delivers 0.50 A of current to a heater, the power consumed by the heater is 10 0.056 W 4.5 W 9.0 W 18 W 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

If a light bulb is rated at 50 W, the amount of energy consumed in 30 minutes is 10 2 kWh 30 kWh 30 J 90,000 J 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

The kilowatt-hour is a unit of 10 current energy potential power 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

A 60 W light bulb illuminated day and night for 30 days consumes ___ of energy, 10 43.2 J 43.2 kWh 1800 kWh 1.5 x 1012 kWh 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

If a family’s electric bill is $74 If a family’s electric bill is $74.00 per month and the cost of electricity is $0.12 per kWh, how much electricity does the family use per month? 10 8.9 kWh 270 kWh 620 kWh 62000 kWh 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Resistance Resistance (R) is a property that determines how much current will flow. Resistance is measured in units called ohms (Ω)

Factors Impacting Resistance Length Resistance increases as length of wire increases. Cross-sectional area Resistance increases as cross-sectional area decreases. Temperature Resistance increases as temperature increases. Material Resistance varies with the material used. silver<copper<gold<aluminum<iron<platinum (in order of increasing resistance)

Ohm’s Law Resistance is equal to potential voltage divided by current. V = I R According to the law, 1 ohm is the resistance permitting an electric charge of 1 A to flow when a potential difference of 1 V is applied across the resistance.

For a wire that obeys Ohm’s Law, the resistance of a wire depends on the ___ the wire. 10 current in length of power delivered by voltage across 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

A battery with a voltage of 9. 0 V is connected to a lamp A battery with a voltage of 9.0 V is connected to a lamp. The current flowing in the circuit is 0.30 A. The resistance of the lamp is 10 0.030 Ω 2.7 Ω 27 Ω 30 Ω 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Length Cross-sectional area Temperature Material What factor impacting resistance explains why light bulbs tend to burn out more frequently when they are first switched on rather than while they are operating? 10 Length Cross-sectional area Temperature Material 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Which wire conducts electricity with the least resistance? 10 One with a large cross-sectional area One with a small cross-sectional area 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

World’s Longest Burning Light Livermore's Centennial Light

Resistors Wires used to complete circuits have low resistance. A wire 1 m in length that is typically used in a physics lab has a resistance of 0.03 Ω. Wires used in home wiring offer as little as 0.004 Ω of resistance for each 1 m of length. Resistors are devices with specific resistances that are used to control current in circuits or parts of circuits. A variable resistor (potentiometer) is used when a smooth, continuous variation of the circuit is desired (example: volume, brightness, contrast, hue, and tone controls on a TV) The human body acts as a variable resistor. (Dry skin has high resistance-wet skin has lower resistance)

A device that can be used to change the current in a circuits in a continuous way is a 10 potentiometer battery motor lamp 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

If a 200 Ω resistor is connected to a 5 V battery, the current in the circuit will be 10 0.025 A 2.5 A 40 A 1000 A 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Types of Circuits There are three types of circuits: Series circuits-all current travels through each device. Parallel circuits-a circuit in which there are several different current paths Combination series-parallel circuit- circuits which includes both series and parallel branches.

Series Circuits In a series circuit, the current is the same throughout. Itotal = IA =IB = IC = … The equivalent resistance (total resistance) of the circuit equals the sum of the individual resistances of the resistors. Rtotal = RA + RB + … The total voltage is the sum of the individual voltages across each device. Vsource = VA + VB + … If the voltage source does not change, adding more devices in series will decrease the current. Because the current flows through one pathway, if one light goes out, they all go out.

The current is ___ in a series circuit. 10 higher at the beginning of the same everywhere lower at the beginning variable in 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

In a series circuit, the equivalent resistance is ___ any single resistance. 10 larger than determined by equal to smaller than 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

If the battery voltage does not change, adding more devices in the series ___ the current. 10 sometimes decreases always decreases sometimes increases always increases 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

To find the current through a series circuit, first calculate the ____. 10 voltage equivalent resistance power equivalent voltage 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Parallel Circuits A parallel circuit is one in which there are several paths. The total current is the sum of the currents through each path. Itotal = IA + IB + Ic + … Placing two or more resistors in parallel always decreases the equivalent resistance of a circuit. 1 = 1 + 1 + 1 + … R RA RB RC The potential difference across each path is the same. Vtotal = VA = VB = VC = …

Safety Devices A short circuit occurs when a circuit with very low resistance is formed. Parallel circuits are susceptible to short circuits. Safety devices are incorporated into the circuit to prevent a circuit overload. 1. Fuse-a piece of metal melts when too much current flows and breaks the circuit. 2. Circuit breaker-an automatic switch that opens when the current reaches a value greater than the rated value in the circuit. 3. Ground-fault interrupter-an outlet that prevents injuries that are caused when an electric appliance falls into water. It contains an electric circuit that detects an extra current path and opens the circuit.

A 16. 0 Ω and a 20. 0 Ω are connected in parallel. 40 A 16.0 Ω and a 20.0 Ω are connected in parallel. 40.0 V is applied to the combination. What is the equivalent resistance? What is the total current in the circuit? What is the current in the 16.0 Ω resistor? What is the power dissipated by the 16.0 Ω resistor?

A heating coil has a resistance of 4.0 Ω and operates on 120 V. What is the current in the coil? What is the power rating of the coil? What energy is supplied to the coil if it is operated for 30 min per day for 30 days? At $.10 per kWh, how much does it cost to operate the coil for 1 month?

A 20.0 Ω, 50.0 Ω, and 10.0 Ω resistor are connected in parallel to each other. 5.5 A of current flows through the 20.0 Ω. Resistor. What is the voltage across the 20.0 Ω resistor? What is the current through the 50.0 Ω resistor? What is the current through the 10.0 Ω resistor? What is the total current through the circuit?

A person has a $5 and a 200 W stereo. At $0.15 per kWh, how many kWh can the person use before the money runs out? How many hours can the person operate the stereo at this rate? If the stereo is plugged into a 120 V outlet, what is the current flowing through the stereo when it is operating? What is the resistance of the stereo?

A 22.0 Ω lamp and a 4.5 Ω lamp are connected in series to a 45 V battery. What is the equivalent resistance of the circuit? What is the current in the circuit? What is the voltage drop across the 22 Ω lamp? What is the power dissipated in the 22.0 Ω lamp?

An ammeter is connected in series to a 10 An ammeter is connected in series to a 10.0 V battery and a 5 Ω and 15 Ω resistor. What should the ammeter read? What is the power dissipated by the circuit? How much energy is supplied by the battery each minute? What is the voltage across each resistor?

The load across a battery consists of two resistors, 15 Ω and 47 Ω, connected in series. What is the equivalent resistance? What is the voltage in the 15 Ω resistor if the current in the circuit is .097 A? What is the voltage in the 47 Ω resistor? What is the voltage of the battery?

A string of 18 identical holiday lights is connected in series to a 120 V source. The string dissipates 64 W. What is the current that flows through the string? What is the equivalent resistance of the light string? What is the resistance of a single light? What power is dissipated by each light?

A 30. 0 Ω resistor is connected in series to two other 30 A 30.0 Ω resistor is connected in series to two other 30.0 Ω resistors connected in parallel. What is the equivalent resistance? If the circuit is connected to a 1.5 V battery, what is the total current that flows through the circuit? How much current flows through the 30.0 Ω that are connected in parallel?

Practice Problem #2 A 30.0 Ω is wired in series with a 20.0 Ω lamp. These two resistors are wired in parallel with 10.0 Ω and 40.0 Ω resistors that are wired in series. All 4 of these resistors are wired in series with a 25.0 Ω resistor and a 25 V battery. Find the total resistance. Find the current through each bulb. Find the voltage drop across each bulb.

The current is the same everywhere throughout the circuit. 10 Parallel Series 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

The total resistance is equal to the sum of the individual resistances. 10 Parallel Series 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

The voltage drop across each resistor in the circuit is the same. 10 Parallel Series 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

The voltage drop is the circuit is proportional to the resistance. 10 Parallel Series 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Adding a resistor to the circuit decreases the total resistance. 10 Parallel Series 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Adding a resistor to the circuit increases the total resistance. 10 Parallel Series 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

If the current through one resistor goes to zero, there is no current in the entire circuit. 10 Parallel Series 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

If the current through one resistor in the circuit goes to zero, the current through all of the other resistors remains the same. 10 Parallel Series 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

This form is suitable for household wiring. 10 Parallel Series 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

An ammeter is connected in ____ in a circuit. 10 Parallel Series 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

A voltmeter is connected in ___ in a circuit. 10 Parallel Series 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

The basic unit of resistance is the 10 volt ohm amp coulomb 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

Electrical force of push is measured in 10 coulombs ohms amps volts 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

A short thick wire has more resistance than a long thin wire. 10 True False 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30

In a DC circuit, current flows from the ___ electrode to the ___ electrode. 10 negative, positive positive, negative positive, positive negative, negative 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30