ELECTRICAL FORCE UNIT NOTES

Transcription

1 ELECTRICAL FORCE UNIT NOTES

2 Property that causes electrical force is called Charge Opposite charges Attract Like charges Repel Charge comes from the atoms. Electrons are negative, protons are positive. Extra electrons make an atom Negative Missing electrons make the atom Positive Coulombs Charge is measured in

3 Charles Coulomb discovered Coulombs Law Electrical Force = K (charge 1)(charge 2) Distance 2 (Distance is squared)

4 Compare to Newton s Law of Gravitation. Both inverse square laws Both direct proportions with the objects Attract Gravitational force always Electrical force can Attract or Repel Coulombs Law important when dealing with very small structures like atoms, & molecules

5 More charge = more Electrical force More Distance = less Electrical force by the distance squared! 2 times the distance = 4 times less or ¼ as much 4 times the distance = 16 times less or 1/16 th as much 4 2 = 16

6 Electrical Forces in everyday life: Heart Electrical impulses make heart work

7 Batteries Separating the positive and negative charges is what gives a battery voltage

8 Copy Machines Electrical charges on the paper attract the ink

9 Lightening Is caused when positive and negative charges build up in the cloud and on the ground

10 2 2 = 4 repel 2 2 = 4 Opposites attract 2 2 = 4 repel 2 3 = 6 Repel 3 2 = 6 attract 2 4 = 8 attract 6 2 = 12 repel 2 2 = 4 repel

11 2 2 = 4 = = 6 = 6 = = 4 = = 6 = 6 = Both repel, (like charges) But 4 is stronger than 1.5 so it repels and moves to the right Left side attracts (opposites) Right side repels (same charge) So it moves left Both opposites so they both attract But 4 is stronger than 2.2 so it moves to the left 2 2 = 4 = = 20 = 20 =

12 Look at the picture below. + 4 Charge on ball (rod) +2 distance between = 4 units a. If the distance between the charges decreases to 2 units, how many times closer is this? 2 times closer b. What happens to the total electrical force between the ball and the post? 2 squared = 4 times more (closer = stronger) c. If the distance goes down to 1 unit apart? How many times closer is this? 4 times closer d. What happens to the total Electrical force between the ball and the post? 4 squared = 16 times more (closer = stronger) repel e. Will the rod attract or repel the ball. Why? same charges

13 Now Do Coulombs Law Practice Worksheet (22 POINTS) In your packet

14 Voltage Difference is the prime mover that causes electricity to flow through a circuit. It is measured in Volts using a Voltmeter Also called Electric Potential Difference in the book Current = flow of charge

15 2 types of Electricity AC - Alternating Current Charge moves back and forth (alternates) In the wire many times a second. Frequency is the rate of change in AC It is measured in Hertz. Main source of AC is generators in power plants, and alternators Used most in our homes volts Direct Current DC - Charge moves in 1 direction. Electrons (which are negative) move from the negative end toward the positive end. Batteries are the most common source. Voltage depends on the size of the battery. 1.5 V 9 V 12 V

16 Ends of Battery are called Electrodes Positive end is the Cathode + like letter t (book is wrong) Anode n for the letter n (book is wrong) Negative end is the Electricity flows out of the negative end toward the positive. Turn to question #35 and 36 in reading guide and put in the correct answers.

17 Question 33 in reading guide, where are they found Electrodes are found on each end (like with AA, C, D) Or they are found on top (9 V, or car battery) 2 or more Batteries can be connected in series to produce more power. You add all the voltages together 6V + 6V = 12V Total of 6 volts Connect positive to negative

18 Electrical systems are made up of: 1. Voltage source (battery or generator) 2. Conductor (wire or printed circuit) 3. Control Elements (switches) 4. Load (user of electricity - lights, motors etc) An electrical circuit is a path closed connected all these (1-4)

19 Schematic Diagram is a drawing that shows the path of electrical current using symbols and pictures or represent the parts. Battery: Light Bulb: or Load (resistor) Switch closed: switch open: Conductor (wires)

20 2 or more loads can be connected in series Vs Voltage source V1 V2 Voltage gets divided Up between loads Vs = V1 + V2 Lights are dim Unscrew one, other goes out (little Christmas lights)

21 2 or more loads can be connected in parallel Each load gets the Full strength of the battery Vs Voltage source V1 V2 Vs = V1 = V2 Lights are bright Unscrew one, the others stay on. House wired in parallel