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Homework Help: Electrostatic physics: can someone check my answers?

  1. Jun 6, 2010 #1
    1. If the potential difference across the nerve of a frog is 85mV and its resistance is 2.5x10^2 Ω what current will flow through the nerve? Answer: 3.4x10^ -4

    2.If all other factors remained the same, what change in resistance would result if the radius of a wire were doubled? Answer: 1.7 x 10

    3. Human hands have a resistance of about 1.0x 10^ 5 Ω when dry and .5x10^3 Ω when wet. When a current of about 1.2mA passes through the body of a person will feel a tingle. The person will lose muscular control (become paralyzed) at a current of about 20mA .suppose the person touches a 120 V wire. Describe the difference in what happens with dry hands and with wet hands. CAUTION: Do not try this. Answer: 1.2 mA

    4. What is the equivalent (total) resistance when resistors have values of 10 Ω 25 Ω and 30 Ω are connected in series? Answer: 65 Ω

    5. Six identical lights are connected in series to a 100 v supply. If the total current flowing is 750 mA ,calculate:

    a) the potential across each bulb Answer: 16.7 v
    b) the resistance of each bulb Answer: 22 Ω
    c) the equivalent resistance of the string of lights Answer: 799.98 Ω

    6. What is the total resistance of a parallel connection of two resistors if one has a resistance of 60 Ω and the other has a resistance of 20 Ω? Answer: 15 Ω

    7. Six identical light bulbs are connected together in parallel. Each bulb has a resistance of 25 Ω. The lights are to be connected to 10v supply.

    a. What is the total resistance of the lights? Answer: 4.2 Ω
    b. What is the total current leaving the power supply? Answer: 2.38 Ω
    c. What is the current through each bulb? Answer: 0.4 A

    8. A parallel combination of three identical resistors has a total resistance of 12 Ω What is the resistance of each resistor? Answer: 4 Ω

    9. Two resistors are connected in parallel. The total resistance of the combination is known to be 6.0 Ω. If one of the resistors is 10 Ω what is the value of the other?
    Answer: 15 Ω

    10. An 800w hair dyer was plugged into a 120 v wall socket. What current will it draw? Answer: 6.7 A

    11. A toy truck uses a 1.5 v cell. If the toy operates at a power of 120 mw, what is its resistance? Answer: 18.75 Ω

    12. A small electric motor has a resistance of 4.5 Ω. If the motor operates using 670 mA of current, what is its power? Answer: 18.75 Ω

    13. What is the total cost of lighting a 60W bulb for 10 minutes? Answer: 51 cent

    14. A coin-operates clothes dryer is rated at 5.0kW and runs for 12 minutes when $1 is inserted. How much is left for the owner after energy costs? Answer: $1

    15. A typical bill for electricity is $70 a month. How much energy in kWh is used?
    Answer: 0.1kwh

    16. A typical nuclear electric power plant has a power of 1.0 GW (10 w). If all the energy produced in a day’s operation were sold, how much money would the plant earn?
    Answer: $ 2.4x10^7

    Thanks for your help...if you can help me correct anything wrong that would be great
  2. jcsd
  3. Jun 12, 2010 #2
    Perhaps you could provide details of your methods?! :smile:
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