Day 12 - Electrical Power and Electrical Energy Consumption

Today we went over the answers to pg 125 in detail on the board. Students were then offered the chance to ask questions about their homework before submitting it. Before doing seatwork, a number of students who didn't pass the Chapter 8 quiz needed to re-take it.



Then we did some more complex practice of Ohm's law, and the rules and calculations of Current, Resistance, and Voltage in parallel and series circuits. Finally we went over two more formulae;

1.) Power (Watts) = Voltage X Current (P =VI)

2.) Electrical Consumption (in Joules ) = Power (Watts) X time (in seconds)

E = Pt

Remember to use the right units, i.e. convert time from minutes or hours into seconds, and on the Chapter 9 Quiz tomorrow (Wednesday), make sure you include the correct units of measure in your answer (volts, watts, amps, etc.).

Today's homework:
Pg 124 #1-7

Worksheet- 3-18

Worksheet- 3-21

Worksheet- 3-23

Worksheet- 3-28

Worksheet- 3-29

Answers

Pg 313 # 1-6

1. A circuit that contains more than one pathway
is called a parallel circuit.

2. When two loads are connected in parallel, the
voltage across each load will be equal.

3. When two loads are connected in parallel, the
current through each load does not have to be
equal.

4. A junction point is the location in a circuit
where the circuit branches into more pathways
or where pathways rejoin.

5. The current entering a junction point must
equal the current leaving the same junction
point.

6. When you add a resistor in parallel to an existing
resistor, the total resistance of the circuit
decreases.

Pg 319 # 1 - 7

1. A parallel circuit contains more than one pathway
for electrons to travel. A series circuit has
only one pathway for electrons to travel.

2. The sum of the voltages lost on each load is
equal to the voltage supplied by the battery.

3. When another resistor is added in series, the
total resistance of the circuit increases.

4. When another resistor is added in parallel, the
total resistance of the circuit decreases.

5. The voltage across the two resistors must be
the same as the battery voltage.

6. The current in one branch of a parallel circuit
is less than the total current entering the junction
point of the circuit.

7. (a) 2.0 A
(b) 6.0 V







Pg 330 # 1-21 Checking Concepts

1. A series circuit contains only one pathway,
whereas a parallel circuit contains more than
one pathway.
2. The current through the second resistor is the
same as the current through the first resistor.
3. The total voltage lost on the three resistors
would be 6.0 V.
4. (a) Increases
(b) Decreases
5. The voltage is the same on both of the
resistors.




6. (a) The total current leaving the junction
point must equal the current entering the
junction point.
(b) The current in the two pathways will be
different.
7. (a) Power is the rate at which energy is transformed.
(b) Power is measured in watts (W).
8. Power is the product of voltage and current:
P = VI.
9. (a) Electrical energy is measured in joules (J)
and kilowatt-hours (kW•h).
(b) The kilowatt-hour is a larger unit.
10. Energy is the product of power and time:
E = Pt.




11. (a) The second bulb goes out.
(b) The result would be different if the bulbs
were connected in parallel. Even if one
bulb “burns out,” there is still a pathway
for current through the second bulb and
therefore it would stay lit.
12. (a) Students’ answers may vary but could
include a car racetrack or a single-lane
bridge.
(b) Students’ answers may vary but could
include multiple checkouts at the supermarket
or entering a bus by two different
doors.
13. (a) The resistors are connected in parallel.
Electrons leaving the battery have two
pathways to return to the battery.
(b) The resistors are connected in series.
Electrons leaving the battery must travel
through both resistors in order to return to
the battery.
14. V1 = 5.0 V, A1 = 2.0 A
15. (a) The current would decrease because
adding another resistor in series increases
the total resistance of the circuit.
(b) The current would increase because adding
another resistor in parallel decreases the
total resistance of the circuit.
16. V1 = 6.0 V, A1 = 2.0 A
17. 144 W
18. 10 A
19. 18 W
20. Lamp 1 = 27 W, Lamp 2 = 18 W
21. Light bulb, hair dryer, microwave oven