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According to Ohm,s law, what happens to circuit current if the applied voltage (a) increases, (b) decreases?
- (a) Current increases
- (b) Current decreases
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According to Ohm,s law, what happens to circuit current if circuit resistance (a) increases, (b) decreases?
- (a) Current decreases
- (b) Current increases
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What is the equation used to find circuit resistance if voltage and current values are known?
R = E\I
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What is the term applied to the rate at which a mechanical or electrical force causes motion?
Power.
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How can the amount of current be changed in a circuit?
By changing the circuit resistance or the voltage of the power source.
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What are the three formulas for electrical power?
P = I*E, P= E^2/R, P = I^2*R
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What is the current in a circuit with 5 ohms of resistance that uses 180 watts of power?
6 amperes. (P = I^2*R) (180 = 6*6*5)
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What is the power used in a circuit that has 10 amperes of current through a 10-ohm resistor?
1 kilowatt.
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How much power is converted by a 1-horsepower motor in 12 hours?
8,952 watt hours or 8.952 kWh.
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What is the efficiency of the motor if it actually uses 9.5 kWh in 12 hours?
942 (rounded to 3 places).
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A series circuit consisting of three resistors has a current of 3 amps. If R1 = 20 ohms, R2= 60 ohms, and R3 = 80 ohms, what is the (a) total resistance and (b) source voltage of the circuit?
- (a). 160 ohms
- (b). 480 volts
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A series circuit consists of two resistors in series. R1 = 25 ohms and R2 = 30 ohms. The circuit current is 6 amps. What is the (a) source voltage, (b) voltage dropped by each resistor, (c) total power, and (d) power used by each resistor?
- (a). 330 volts
- (b). E1 = 150 volts, E2 = 180 volts
- (c). 1.98 kilowatts
- (d). P1 = 900 watts, P2 = 1.08 kilowatts
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When using Kirchhoff ,s voltage law, how are voltage polarities assigned to the voltage drops across resistors?
The point at which current enters the resistor is assigned a negative polarity and the point at which current leaves the resistor is assigned a positive polarity.
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A circuit has a source voltage of 100 volts and two 50-ohm resistors connected in series. If the reference point for this circuit is placed between the two resistors, what would be the voltage at the reference point?
50 volts.
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What is an open circuit?
A circuit where there is no longer a complete path for current flow.
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What is a short circuit?
An accidental path of low resistance which passes an abnormally high amount of current.
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Why will a meter indicate more voltage at the battery terminal when the battery is out of a circuit than when the battery is in a circuit?
The internal (source) resistance of the battery will drop some of the voltage.
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What condition gives maximum power transfer from the source to the load?
When the load resistance equals the source resistance.
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A circuit has a source voltage of 25 volts. The source resistance is 1 ohm and the load resistance is 49 ohms. What is the efficiency of power transfer?
98 percent (12.25 watts/12.5 watts x 100)
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There is a relationship between total current and current through the individual components in a circuit. What is this relationship in a series circuit and a parallel circuit?
Total current in a series circuit flows through every circuit component but in a parallel circuit total current divides among the available paths.
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In applying Kirchhoff's current law, what does the polarity of the current indicate?
Whether the current is entering the junction (+) or leaving the junction (-).
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Four equal resistors are connected in parallel, each resistor has an ohmic value of 100 ohms, what is the equivalent resistance?
25 ohms (Req = R/N)
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Three resistors connected in parallel have values of 12 k ohms, 20 k ohms, and 30 k ohms. What is the equivalent resistance?
6k ohms
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Two resistors connected in parallel have values of 10 k ohms and 30 k ohms. What is the equivalent resistance?
7.5k ohms
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What term identifies a single resistor that represents total resistance of a complex circuit?
Equivalent resistor or Req.
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The total power in both series and parallel circuits is computed with the formula: PT = P1 + P2 + P3 +...Pn. Why can this formula be used for both series and parallel circuits?
In both cases all the power used in the circuit must come from the source.
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A circuit consists of three resistors connected in parallel across a voltage source. Rl = 40O, R2 = 30O, R3 = 40O, and PR3 = 360 watts. Solve for RT, ES and IR2. (Hint: Draw and label the circuit first.)
- RT = 12 ohms
- ES = 120 volts
- IR2 = 4A
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What is the effect on total resistance and total current in a circuit if an open occurs in (a) a parallel branch, and (b) in a series portion?
- (a) Total resistance increases, total current decreases
- (b) Total resistance becomes infinite, total current is equal to zero
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What is the effect on total resistance and total current in a circuit if a short occurs in (a) a parallel branch, and (b) in a series portion?
- (a) Total resistance decreases, total current increases
- (b) Total resistance decreases, total current increases
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If one branch of a parallel network is shorted, what portion of circuit current flows through the remaining branches?
None.
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What information must be known to determine the component values for a voltage divider?
The source voltage and load requirements (voltage and current).
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If a voltage divider is required for a load that will use 450 mA of current, what should be the value of bleeder current?
45 mA. rule-of-thumb.
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If the load requirement consists of both positive and negative voltages, what technique is used in the voltage divider to supply the loads from a single voltage source?
The ground (reference point) is placed in the proper point in the voltage divider so that positive and negative voltages are supplied.
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Is it considered safe for a person to touch any energized low-voltage conductor with the bare hand?
NEVER! All energized electric circuits should be considered potentially dangerous.
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What should you do if you become aware of a possible malfunction in a piece of electrical equipment?
You should immediately report this condition to a qualified technician.
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Who should perform CPR?
Only trained, qualified personnel.
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