New Zealand NZART pool, section ZLB07

Subelement ZLB

Basic Electrical Theory

Section ZLB07

Power calculations

ZLB0701

A transmitter power amplifier requires 30 mA at 300 volt. The DC input power is

A.
300 watt
B.
9000 watt
Correct Answer
C.
9 watt
D.
6 watt

ZLB0701

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ZLB0702

The DC input power of a transmitter operating at 12 volt and drawing 500 milliamp would be

Correct Answer
A.
6 watt
B.
12 watt
C.
20 watt
D.
500 watt

ZLB0702

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ZLB0703

When two 500 ohm 1 watt resistors are connected in series, the maximum total power that can be dissipated by both resistors is

A.
4 watt
Correct Answer
B.
2 watt
C.
1 watt
D.
1/2 watt

ZLB0703

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ZLB0704

When two 1000 ohm 5 watt resistors are connected in parallel, they can dissipate a maximum total power of

A.
40 watt
B.
20 watt
Correct Answer
C.
10 watt
D.
5 watt

ZLB0704

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ZLB0705

The current in a 100 kilohm resistor is 10 mA. The power dissipated is

A.
1 watt
Correct Answer
B.
10 watt
C.
100 watt
D.
10,000 watt

ZLB0705

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ZLB0706

A current of 500 milliamp passes through a 1000 ohm resistance. The power dissipated is

A.
0.25 watt
B.
2.5 watt
C.
25 watt
Correct Answer
D.
250 watt

ZLB0706

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ZLB0707

A 20 ohm resistor carries a current of 0.25 ampere. The power dissipated is

Correct Answer
A.
1.25 watt
B.
5 watt
C.
2.50 watt
D.
10 watt

ZLB0707

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ZLB0708

If 200 volt is applied to a 2000 ohm resistor, the resistor will dissipate

Correct Answer
A.
20 watt
B.
30 watt
C.
10 watt
D.
40 watt

ZLB0708

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ZLB0709

The power delivered to an antenna is 500 watt. The effective antenna resistance is 20 ohm. The antenna current is

A.
25 amp
B.
2.5 amp
C.
10 amp
Correct Answer
D.
5 amp

ZLB0709

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ZLB0710

The unit for power is the

A.
ohm
Correct Answer
B.
watt
C.
ampere
D.
volt

ZLB0710

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ZLB0711

The following two quantities should be multiplied together to find power

A.
resistance and capacitance
Correct Answer
B.
voltage and current
C.
voltage and inductance
D.
inductance and capacitance

ZLB0711

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ZLB0712

The following two electrical units multiplied together give the unit "watt"

Correct Answer
A.
volt and ampere
B.
volt and farad
C.
farad and henry
D.
ampere and henry

ZLB0712

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ZLB0713

The power dissipation of a resistor carrying a current of 10 mA with 10 volt across it is

A.
0.01 watt
Correct Answer
B.
0.1 watt
C.
1 watt
D.
10 watt

ZLB0713

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ZLB0714

If two 10 ohm resistors are connected in series with a 10 volt battery, the battery load is

Correct Answer
A.
5 watt
B.
10 watt
C.
20 watt
D.
100 watt

ZLB0714

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ZLB0715

Each of 9 resistors in a circuit is dissipating 4 watt. If the circuit operates from a 12 volt supply, the total current flowing in the circuit is

A.
48 ampere
B.
36 ampere
C.
9 ampere
Correct Answer
D.
3 ampere

ZLB0715

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ZLB0716

Three 18 ohm resistors are connected in parallel across a 12 volt supply. The total power dissipation of the resistor load is

A.
3 watt
B.
18 watt
Correct Answer
C.
24 watt
D.
36 watt

ZLB0716

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ZLB0717

A resistor of 10 kilohm carries a current of 20 mA. The power dissipated in the resistor is

A.
2 watt
Correct Answer
B.
4 watt
C.
20 watt
D.
40 watt

ZLB0717

By convention, \(P\) is power, \(I\) is current, \(R\) is resistance, and \(E\) is Voltage (Electro-motive force).

The Power Law states: \(P = I \times E\). Ohm's law states that \(E = I \times R\). Combining those to remove E, we get a restatement of the Power Law as \(P = I \times (I \times R)\), or \(P = I^2 \times R\)

So in this case:

\[P = (.02)^2 \times 10,000\] \[P = 0.0004 \times 10,000\]

Thus

\[P = 4 \text{ watts}\]

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ZLB0718

A resistor in a circuit becomes very hot and starts to burn. This is because the resistor is dissipating too much

A.
current
B.
voltage
C.
resistance
Correct Answer
D.
power

ZLB0718

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ZLB0719

A current of 10 ampere rms at a frequency of 50 Hz flows through a 100 ohm resistor. The power dissipated is

A.
500 watt
B.
707 watt
Correct Answer
C.
10,000 watt
D.
50,000 watt

ZLB0719

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ZLB0720

The voltage applied to two resistors in series is doubled. The total power dissipated will

Correct Answer
A.
increase by four times
B.
decrease to half
C.
double
D.
not change

ZLB0720

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