Circuits, Volts, Amps, Circuits, Volts, Amps, and Resistanceand Resistance

Series circuitsSeries circuits

Simple circuits that have only one path for Simple circuits that have only one path for the current to flow are called the current to flow are called series series circuits.circuits.

Series circuits can be compared to that of Series circuits can be compared to that of a race track. a race track.

Parallel CircuitsParallel Circuits

Parallel circuitsParallel circuits are circuits that allow are circuits that allow electricity to flow in multiple paths.electricity to flow in multiple paths.

Parallel circuits are more like city streets Parallel circuits are more like city streets than a race track. They give the electricity than a race track. They give the electricity options for movement.options for movement.

The BatteryThe Battery

Batteries contain stored electric potential Batteries contain stored electric potential energy from chemical reactions that go on energy from chemical reactions that go on inside the battery.inside the battery.

A good example of the reaction is:A good example of the reaction is:

Zn + Cu Zn + Cu 2+2+ = Zn = Zn 2+2+ + Cu + Cu

The battery provides the potential energy The battery provides the potential energy to do “to do “workwork””

In order to do this “work” the battery must In order to do this “work” the battery must be connected in a closed circuitbe connected in a closed circuit

Energy is measured in “Energy is measured in “JoulesJoules””

The energy that is stored in the battery is The energy that is stored in the battery is also measured in Joules.also measured in Joules.

Potential energy difference is measured in Potential energy difference is measured in JoulesJoules per per CoulombCoulomb or or VoltsVolts..

Therefore:Therefore:V = V = EE

QQ

SoSo

Potential energy difference = Potential energy difference = the amount of stored energythe amount of stored energy

chargecharge

We can measure potential energy We can measure potential energy difference using a difference using a voltmetervoltmeter. The . The measure is in measure is in voltsvolts..

V

The voltmeter must be put in parallel with The voltmeter must be put in parallel with the circuit. the circuit.

This means it must create it’s own This means it must create it’s own separate loop in the circuit to work separate loop in the circuit to work properly.properly.

The voltmeter will measure the difference The voltmeter will measure the difference at one point on the circuit and compares it at one point on the circuit and compares it to another point on the circuit.to another point on the circuit.

The AmmeterThe Ammeter

An ammeter measures current through the An ammeter measures current through the circuit. It measures ampscircuit. It measures amps

Think about current as the speed that the Think about current as the speed that the charges travel, an ammeter is like a speed charges travel, an ammeter is like a speed radar gun for electricity.radar gun for electricity.

A

An ammeter must be put in series to work An ammeter must be put in series to work properly.properly.

ResistanceResistance

What does it mean to “resist”?What does it mean to “resist”?

What would be harder? What would be harder?

1.1. Pushing a 50kg box across carpet?Pushing a 50kg box across carpet?

2.2. Pushing a 50kg box across tile floors?Pushing a 50kg box across tile floors?

ResistanceResistance is the property of a substance is the property of a substance to hinder motion. to hinder motion.

A A resistorresistor converts electric energy into converts electric energy into other forms of energy (heat, light) other forms of energy (heat, light)

Resistance is the Resistance is the ratio ratio of potential energy of potential energy difference (voltage) across a difference (voltage) across a loadload, to the , to the current through the current through the loadload

Resistance = Resistance = VoltageVoltage

CurrentCurrent

Resistance is measured in Ohms or Resistance is measured in Ohms or ΩΩ

Ohm’s LawOhm’s Law

This equation is referred to as Ohm’s LawThis equation is referred to as Ohm’s Law

Where V = IRWhere V = IR

V

IR

If we had a voltmeter and a If we had a voltmeter and a ammeter we could measure the ammeter we could measure the

resistanceresistance

Example QuestionExample Question

What is the resistance of the heating coil of an What is the resistance of the heating coil of an electric heater, if a current of 12.5A runs through electric heater, if a current of 12.5A runs through it, when connected to a wall outlet of 120V?it, when connected to a wall outlet of 120V?

Given:Given:

Solution:Solution:

Paraphrase:Paraphrase:

Example QuestionExample Question

What is potential difference (voltage) across a light What is potential difference (voltage) across a light bulb that has a resistance of 3ohms and a bulb that has a resistance of 3ohms and a current of 1.5Acurrent of 1.5A

Given:Given:

Solution:Solution:

Paraphrase:Paraphrase:

Factors that effect resistanceFactors that effect resistance

1.1. Length – resistance increases with Length – resistance increases with lengthlength

2.2. Cross sectional area – resistance Cross sectional area – resistance decreases when area increasesdecreases when area increases

3.3. Temperature – resistance increases Temperature – resistance increases when temperature decreaseswhen temperature decreases

4.4. Material – some metals allow electrons Material – some metals allow electrons to move more freely than othersto move more freely than others

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1.1. In your own words explain In your own words explain electrical resistance.electrical resistance.2.2. What is the formula for resistance and what units are What is the formula for resistance and what units are

equivalent to the ohm?equivalent to the ohm?3.3. List 3 characteristics of a wire that affect its resistance.List 3 characteristics of a wire that affect its resistance.4.4. A light bulb passes a current of 0.83 A when the A light bulb passes a current of 0.83 A when the

potential difference is 120V. What is the bulb’s potential difference is 120V. What is the bulb’s resistance?resistance?

5.5. What is the potential difference across an electric What is the potential difference across an electric water heater element that has a resistance of 32ohms water heater element that has a resistance of 32ohms when a current through it is 6.8 A?when a current through it is 6.8 A?

6.6. Matt says that if the resistance of a load becomes Matt says that if the resistance of a load becomes larger, the current must become larger as well. larger, the current must become larger as well. Melissa explains that the current should decrease. Melissa explains that the current should decrease. Who is correct? Explain.Who is correct? Explain.