Technician Class Series – It’s the Law, Per Mr. OHM

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Hello everybody and welcome back to Everything Hamradio! Today we are going to continue our series on the Technician Class License Question Pool! Today we will be talking about Ohm’s Law.

As always, the correct answers will be in bold. I also recommend that you only read the correct answers when studying for your test. If you do this, when you take your test and you see a question, there will be a better chance that the correct answer will jump out at you easier. Some say that this approach is kind of like cheating, but the way that I see it, you will always be learning something in this hobby and you don’t have to know everything there is to know about the hobby to get your license.

If you would like to purchase a copy of the Technician Class study book, written by Gordon West, WB6NOA with Eric P. Nichols, KL7AJ, that this series is loosely based around, below is a link to it.

Let’s move on to the good stuff, shall we?


T5A10 Which term describes the rate at which electrical energy is used?

  1. Resistance
  2. Current
  3. Power
  4. Voltage

Power is the term that describes the rate of electrical energy that is used. If you look at your electric meter outside your home, there is a little disk(more than likely) that will be spinning and either a digital readout or several dials. This meter is measuring how many watts you are currently using in your house. It determines the amount of power you are using by multiplying the voltage by the current that you are using.

 

T5A02 Electrical power is measured in which of the following units?

  1. Volts
  2. Watts
  3. Ohms
  4. Amperes

Electrical power is measured in Watts. Any electrical device requires a certain amount of wattage to work. Wattage is also used to determine Power. We use power wattage when we talk about how much power we are transmitting out to our antennas. We also use it to determine if our power supply is big enough to power the equipment that we have. If all the equipment is turned on at the same time and requires 500 watts of power but our power supply only puts out 400 watts, then something is not going to come on or at the very least is going to go off, especially when you key up your radio to transmit and your needed incoming power increases.

 

T5C08 What is the formula used to calculate electrical power in a DC circuit?

  1. Power (P) equals voltage (E) multiplied by current (I)
  2. Power (P) equals voltage (E) divided by current (I)
  3. Power (P) equals voltage (E) minus current (I)
  4. Power (P) equals voltage (E) plus current (I)

ohmslaw3

Using this picture you can figure out what the formula is for figuring out what the power is, or the voltage or current. Take your finger and cover up the thing that you want to figure out. The two values that are left you will either multiply together if they are side by side, Voltage(E) X Current(I). If the values are above and below each other,then you would divide, Power(P) divided by Voltage(E) or Power(P) divided by Current(I) depending on what you are trying to solve for.

 

T5C09 How much power is being used in a circuit when the applied voltage is 13.8 volts DC and the current is 10 amperes?

  1. 138 watts
  2. 0.7 watts
  3. 23.8 watts
  4. 3.8 watts

Using the picture on the last question what would be the formula? P = E X I. Correct! So:

P = E x I
P = 13.8(Volts) X 10(Amps)
P = 138 Watts

 

T5C10 How much power is being used in a circuit when the applied voltage is 12 volts DC and the current is 2.5 amperes?

  1. 4.8 watts
  2. 30 watts
  3. 14.5 watts
  4. 0.208 watts

Again what would the formula be?

P = E x I
P = 12(E) x 2.5(I)
P = 30 Watts

 

T5C11 How many amperes are flowing in a circuit when the applied voltage is 12 volts DC and the load is 120 watts?

  1. 0.1 amperes
  2. 10 amperes
  3. 12 amperes
  4. 132 amperes

With this question the formula changes. So use Ohms law here and figure out the formula.

I = P / E
I = 120(P) / 12(E)
I = 10 Amperes

 

T5D02 What formula is used to calculate voltage in a circuit?

  1. Voltage (E) equals current (I) multiplied by resistance (R)
  2. Voltage (E) equals current (I) divided by resistance (R)
  3. Voltage (E) equals current (I) added to resistance (R)
  4. Voltage (E) equals current (I) minus resistance (R)

ohmslaw3

Using this picture you can figure out what the formula is for figuring out what the voltage is, or the resistance or current. Take your finger and cover up the thing that you want to figure out. The two values that are left you will either multiply together if they are side by side, Resistance(R) x   Current(I). If the values are above and below each other, then you would divide, Voltage(E) divided by Current(I) or Voltage(E) divided by Resistance(R) depending on what you are trying to solve for.

 

T5D10 What is the voltage across a 2-ohm resistor if a current of 0.5 amperes flows through it?

  1. 1 volt
  2. 0.25 volts
  3. 2.5 volts
  4. 1.5 volts

In this question, you are looking for voltage so take your finger and cover up Voltage and what is you formula?

E = R x I
E = 2(R) x 0.5(I)
E = 1(E)

 

T5D11 What is the voltage across a 10-ohm resistor if a current of 1 ampere flows through it?

  1. 1 volt
  2. 10 volts
  3. 11 volts
  4. 9 volts

Again we are solving for Voltage.

E = R x I
E = 10(R) x 1(I)
E = 10(E)

 

T5D12 What is the voltage across a 10-ohm resistor if a current of 2 amperes flows through it?

  1. 8 volts
  2. 0.2 volts
  3. 12 volts
  4. 20 volts

E = R x I
E = 10(R) x 2(I)
E = 20(E)

 

T5D01 What formula is used to calculate current in a circuit?

  1. Current (I) equals voltage (E) multiplied by resistance (R)
  2. Current (I) equals voltage (E) divided by resistance (R)
  3. Current (I) equals voltage (E) added to resistance (R)
  4. Current (I) equals voltage (E) minus resistance (R)ohmslaw3

Look at the Ohms Law Picture again. This time we are going to put our finger over Current(I). Since Voltage(E) is above Resistance(R), the formula will be I = V / R or Current(I) equals voltage(E) divided by Resistance(R).

 

T5D09 What is the current flowing through a 24-ohm resistor connected across 240 volts?

  1. 24,000 amperes
  2. 0.1 amperes
  3. 10 amperes
  4. 216 amperes

Using the formula to find Current, let’s figure this question out:

I = E / R
I = 240(E) / 24(R)
I = 10(I)

 

T5D08 What is the current flowing through a 100-ohm resistor connected across 200 volts?

  1. 20,000 amperes
  2. 0.5 amperes
  3. 2 amperes
  4. 100 amperes

I = E / R
I = 200(E) / 100(R)
I = 2(I)

 

T5D07 What is the current flow in a circuit with an applied voltage of 120 volts and a resistance of 80 ohms?

  1. 9600 amperes
  2. 200 amperes
  3. 0.667 amperes
  4. 1.5 amperes

I = E / R
I = 120(E) / 80(R)
I = 1.2(I)

 

T5D08 What is the current flowing through a 100-ohm resistor connected across 200 volts?

  1. 20,000 amperes
  2. 0.5 amperes
  3. 2 amperes
  4. 100 amperes

I = E / R
I = 200(E) / 100(R)
I = 2 (I)

 

T5D07 What is the current flow in a circuit with an applied voltage of 120 volts and a resistance of 80 ohms?

  1. 9600 amperes
  2. 200 amperes
  3. 0.667 amperes
  4. 1.5 amperes

I = E / R
I = 120(E) / 80(R)
I = 1.5(I)

 

T5D03 What formula is used to calculate resistance in a circuit?

  1. Resistance (R) equals voltage (E) multiplied by current (I)
  2. Resistance (R) equals voltage (E) divided by current (I)
  3. Resistance (R) equals voltage (E) added to current (I)
  4. Resistance (R) equals voltage (E) minus current (I)ohmslaw3

Using the Ohms Law picture, put your finger over Resistance(R) and what is the formula that it makes? Resistance(R) = Voltage(E) / Current(I) or Resistance(R) equals Voltage(E) divided by Current(I).

 

T5D04 What is the resistance of a circuit in which a current of 3 amperes flows through a resistor connected to 90 volts?

  1. 3 ohms
  2. 30 ohms
  3. 93 ohms
  4. 270 ohms

R = E / I
R = 90(E) / 3(I)
R = 30(R)

 

T5D05 What is the resistance in a circuit for which the applied voltage is 12 volts and the current flow is 1.5 amperes?

  1. 18 ohms
  2. 0.125 ohms
  3. 8 ohms
  4. 13.5 ohms

R = E / I
R = 12(E) / 1.5(I)
R = 8(R)

 

T5D06 What is the resistance of a circuit that draws 4 amperes from a 12-volt source?

  1. 3 ohms
  2. 16 ohms
  3. 48 ohms
  4. 8 Ohms

R = E / I
R = 12(E) / 4(I)
R = 3(R)


So that brings us to the end of this section. Next week we will be talking about Emergencies! Please share my site with your friends and if you have not done so already, please subscribe to my email list to get notified on when I publish a new post. Please Like me on Facebook, and follow me on Twitter, Google+, LinkedIn and StumbledUpon. Links to all of these can be found under social on the menu.

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Until next time…

73 de Curtis, K5CLM

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