# Recent questions and answers in Basic concepts

If an incandescent lamp of 80 ohms resistance takes a current of 0.75 ampere, what voltage is required to light it? A.45 volts B.60 volts c.23 volts D.None of these

The hot resistance of the bulb's filament is higher than its cold resistance because the temperature co-efficient of the filament is?

Heat in a conductor is produced on the passage of electric current due to?

State and explain Ohm's law for magnetic circuit.

An ideal power supply consist of   (A) Very small output resistance (B) Zero Internal resistance (C) Very large input resistance (D) Very large output resistance

When a sine wave has a frequency of 100 Hz in 12 s it goes through? A.1/100 cycle B.12 cycles C.120 cycles D.1,200 cycles

In order to get maximum power transfer from a capacitive source, the load must? A.have a capacitive reactance equal to circuit resistance B.have an impedance that is the complex conjugate of the source impedance C.be as capacitive as it is inductive D.none of the above

Fourteen milliamperes can be expressed as? A.14 MA B.14 μA C.14 kA D.14 mA

How much voltage is needed to produce 2.5 A of current through a 200 ohms resistor? A.50 V B.500 V C.80 V D.8 V

When there is 12 mA of current through a 1.2 k ohms resistor, the voltage across the resistor is? A.14.4 V B.1.4 V C.100 V D.10 V

How much resistance is needed to draw 17.6 mA from a 12 volt source? A.212 ohms B.6.8 kohms C.68 ohms D.680 ohms

When placed close together, two positively charged materials will? A.attract B.become neutral C.become negative D.repel

The colored bands for a 4,700 ohm resistor with a ten percent tolerance are? A.yellow, violet, red, gold B.yellow, violet, orange, gold C.yellow, violet, red, silver D.orange, violet, red, silver

A certain appliance uses 350 W. If it is allowed to run continuously for 24 days, how many kilowatt- hours of energy does it consume? A.20.16 kWh B.201.6 kWh C.2.01 kWh D.8.4 kWh

When the turns ratio of a transformer is 20 and the primary ac voltage is 12 V, the secondary voltage is? A.12 V B.120 V C.240 V D.2,400 V

In a certain loaded transformer, the secondary voltage is one-fourth the primary voltage. The secondary current is? A.one-fourth the primary current B.four times the primary current C.equal to the primary current D.one-fourth the primary current and equal to the primary current

In a Y-connected circuit, the magnitude of each line current is? A.one-third the phase current B.three times the corresponding phase current C.equal to the corresponding phase current D.zero

The primary coil of a transformer is connected to a 60 V ac source. The secondary coil is connected to a 330 ohms load. The turns ratio is 3:1. What is the secondary voltage? A.2 V B.20 V C.180 V D.18 V

The turns ratio required to match an 80 ohms source to a 320 ohms load is? A.80 B.20 C.4 D.2

When the pointer of an analog ohmmeter reads close to zero, the resistor being measured is? A.overheated B.shorted C.open D.reversed

A resistance of 3.3 M ohms is connected across a 500 V source. The resulting current is approximately? A.15.1 μA B.151 μA C.66 mA D.660 mA

The formula to find I when the values of V and R are known is? A.I = VR B.I = R/V C.V = IR D.I = V/R

When converting 0.16 mA to microamperes, the result is? A.16 μA B.160 μA C.1,600 μA D.0.0016 μA

The average value of a 12 V peak sine wave over one complete cycle is? A.0 V B.1.27 V C.7.64 V D.6.37 V

Two series resistors are connected to an ac source. If there are 7.5 V rms across one resistor and 4.2 V rms across the other, the peak source voltage is? A.16.54 V B.1.65 V C.10.60 V D.5.93 V

A certain transformer has 400 turns in the primary winding and 2,000 turns in the secondary winding. The turns ratio is? A.0.2 B.0.4 C.5 D.25

If it takes 400 ms to use 12,000 J of energy, the power is? A.30 kW B.30 W C.3 W D.300 kW

A material that does not allow current under normal conditions is a(n)? A.insulator B.conductor C.semiconductor D.valence

Current flows in a circuit when? A.a switch is opened B.a switch is closed C.the switch is either open or closed D.there is no voltage

Four amperes of current are measured through a 24 ohms resistor connected across a voltage source. How much voltage does the source produce? A.960 V B.9.6 V C.96 V D.8 V

You are measuring the current in a circuit that is operated on an 18 V battery. The ammeter reads 40 mA. Later you notice the current has dropped to 20 mA. How much has the voltage changed? A.9 V B.900 mV C.0 V D.18 V

How much resistance is required to limit the current from a 12 V battery to 3.6 mA? A.3.3 k ohms B.33 k ohms C.2.2 k ohms D.22 k ohms

The number of millivolts in 0.06 kilovolts is? A.600 V B.6,000 mV C.60,000 mV D.600,000 mV

A sine wave of 15 kHz is changing at a faster rate than a sine wave with a frequency of? B.12 kHz C.18 kHz D.1.3 MHz

If a transformer has 50 turns in the primary winding and 10 turns in the secondary winding, what is the reflective resistance if the secondary load resistance is 250 ohms? A.250 ohms B.25 ohms C.6,250 ohms D.62,500 ohms

How many watt-hours represent 65 W used for 18 h? A.11.7 Wh B.1,170 Wh C.11,700 Wh D.117,000 Wh

In 0.025 W, there are? A.25 kW B.0.00025 mW C.2,500 μW D.25 mW

A two-terminal variable resistor is known as a? A.potentiometer B.thermistor C.rheostat D.wiper

The minimum resistance value for a blue, gray, red, silver resistor is? A.612 ohms B.6,120 ohms C.6,800 ohms D.6,460 ohms

Twelve volts are applied across a resistor. A current of 3 mA is measured. What is the value of the resistor? A.4 ohms B.400 ohms C.4 kohms D.4.4 ohms

Approximately how many milliamperes of current flow through a circuit with a 40 V source and 6.8 k ohms of resistance? A.27.2 mA B.59 mA C.5.9 mA D.590 mA

When converting 7,000 nA to microamperes, the result is? A.0.007 μA B.0.7 μA C.700 μA D.7 μA

If the peak value of a sine wave is 30 V, the rms value is? A.19.08 V B.7.07 V C.0.707 V D.23.10 V