Name: _________________________________________________ Date: ______________________ Worksheet 1-1 1. What are the three principal parts of an atom, and what charge does each part carry? 2. How many times smaller is an electron than a proton? 3. How many times more does a proton weigh than an electron? 4. What is the Law of Charges? 5. How many valence electrons are generally contained in materials used for conductors? 6. How many valence electrons are generally contained in materials used for insulators? 7. What is electricity? 8. What is a gluon? 9. It is theorized that protons and neutrons are actually formed from a combination of smaller particles. What are these particles called? 10. What is a coulomb? 11. What is an ampere? 12. What is voltage? 13. What is an ohm? 14. What is a watt? 15. What is a volt-ampere? Now let’s try a little Ohm’s Law math, shall we? Ohm’s Law simply states that in a DC circuit, the current is directly proportional to the voltage and inversely proportional to the resistance. In other words, it will take 1 volt to push 1 ampere through 1 ohm of resistance. If the resistance of a circuit remains constant and we increase voltage, current will increase. Likewise, if the resistance remains constant and voltage decreases, so does current. However, if voltage remains constant and resistance is increased, there is a decrease in current, and if we decrease the resistance, the current increases. Name: _________________________________________________ Date: ______________________ Worksheet 1-1 Let’s try it and see what happens: If I have a circuit that has a resistance of 50 ohms and a current flow of 2 amperes, per Ohm’s Law, where E = I x R, the voltage connected must be 100 volts. If I have 120 volts attached to a 30 ohm load, Ohm’s Law tells me that I = E/R, so the amount of current flow must be 4 amperes. Finally, if I have 240 volts at 10 amperes, Ohm’s Law says that R= E/I, which means that I have a resistance of 24 ohms. Also note that if we’re looking for watts, we need to multiply volts times amperes. So a 120 watt lightbulb powered by 120 volts is drawing 1 ampere. Now, let’s try it out. Please show your work: 1. An electric heating element has a resistance of 16 ohms and is connected to a voltage of 120 volts. How much current will flow in this circuit? 2. How many watts of heat are being produced by the heating element in Question 1? 3. A 240 volt circuit has a current flow of 20 amperes. How much resistance is connected in the circuit? 4. An electric motor has an apparent resistance of 15 ohms. If 8 amperes of current are flowing through the motor, what is the connected voltage? 5. A 240 volt air conditioning compressor has an apparent resistance of 8 ohms. How much current will flow in the circuit? 6. How much power is being used by the motor in Question 5? 7. A 5 kilowatt electric heating unit is connected to a 240 volt line. What is the current flow in the circuit? 8. If the voltage in Question 7 is reduced to 120 volts, how much current would be needed to produce the same amount of power? 9. Is it less expensive to operate the electric heating unit in Question 7 on 240 volts or on 120 volts? Explain your answer. Name: _________________________________________________ Date: ______________________ Worksheet 1-1 How about some practical problems? 1. The blueprint you’re working from shows eight 500 watt lamps are to be installed on the same circuit. Circuit voltage is 277 volts, and the print shows them on a 20 ampere circuit breaker. Knowing that under continuous duty conditions, the breaker can only be loaded to 80% of its rating, is the 20 ampere breaker sufficient to carry the circuit load? Please show your math. 2. You need to install five ceiling fans with light kits in a new home. The light kits have four 60 watt bulbs, and the fans draw 1.8 amperes at high speed. They are considered continuous duty because it is assumed they can be operated for more than 3 hours at a time. The fans are to be connected to 15 ampere circuits. How many fans could be on one 15 ampere circuit? How many circuits will be required to supply all five fans? 3. You’re installing a swimming pool. You need to run a circuit for a 600 watt underwater light and a circulating pump. The pump motor nameplate says that the pump will draw 8.5 amperes when running at full load. Both devices are considered continuous duty. Is it possible to wire both devices on a single 20 ampere circuit?
