Science Resistance Worksheet

 

Noah Nishihara Homegroup 909                                                               Tuesday, 3 November 2015     

Questions on Electricity

1.The completed table:

 

Symbol

Unit

Measured using…

Voltage

V

V, J/C

Volts,Joules per coulomb

Current (Intensity)

I, i

A

Amperes

Resistance

R, r

Ω

Ohms

2.a All materials offer some resistance to electricity.

b A conductor has lowresistance and an insulator has highresistance.
c  If the resistance in a circuit is increased the current becomes low/less. I=V/R

3. Ohm’s Law    V=I×R             I=       R=

Voltage (Volts)

Current (amps)

Resistance (ohms)

15

5

3

6

3

2

240

12

20

110

5.7894736842105263157894736842105

19

4. The resistance of the heating element in the toaster is 240/4 which is 60 ohms.

5.a P= 0.12 kilowatts; t= 12 hours; E= Pt= 0.12 kilowatts×12 hours= 1.44 kilowatt-hours

b P= 0.12 kilowatts; t= 9 hours; E= 1.08 kilowatt-hours

c P= 0.48 kilowatts; t= 5 hours; E= 2.4 kilowatt-hours

d P= 1.5 kilowatts; t= 0.16667 hours; E= 0.250005 kilowatt-hours

6.a The appliance that uses the most electrical energy per second is the hot water system.

b Leaving on a bar heater would be more expensive.

c The calculator, clock, portable radio and perhaps the personal computer are run by batteries.

Their power consumption is less than the plugged in appliances.

dStoves and hot water systems have their own circuit and circuit-breaker due to its high energy consumption; for safety and to differentiate it from the usual household appliances.

7.8 kilowatts for 30 minutes (0.5 hours) Amount of electricity Kaori used: 4 kWh

8. The reading on this meter is 4612 kWh.

9. 0.3 kilowatts for 3 hours a day. 0.9 kilowatt-hours. Cost of running the TV for a year: 13.5 cents × 365= 4927.5 cents

10. a 4H has the greatest resistance due to its hardness and thinness.

b 3B has the most graphite as it is thick and soft which allows more current to flow through.

Challenge

1 The element in the toaster becomes red hot due to its high resistance. The wires outside the toaster remain cool as it does not have the same amount of resistance.

2 Sweat contains salt and allows the skin to lower its resistance to electricity. Lie-detectors detect the difference in conductivity between no sweat and sweat being on the skin.

3 a 0.0048 amps is less than 0.01 amps therefore no death. b0.00012 amps is even less than before therefore no danger. c 0.1 amps means that she would be in danger. d Any path that does not pass through near the heart is considered better than a path passing through the heart.

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