# ASVAB Electronics Practice Test 1

#### Electrical power can be calculated with the following formula: P = I x V What does the letter I represent in this formula?

P represents power, which is measured in watts. I represents current, which is measured in amperes. V represents voltage which is measured in volts.

#### What is the load in this basic circuit model?

In a basic circuit model, there is a voltage source (pictured here as a battery at points A and B), a load, and conductors. The conductors are drawn using the lines and arrows. The load in this model is the light bulb pictured at point C. Examples of loads are light bulbs, resistors and motors.

#### Three amps equals how many milliamps?

A milliamp is one thousandth of an amp. So every amp equals 1,000 milliamps: 3 x 1,000 = 3,000.

#### What type of electrical circuit is depicted above?

A series-parallel circuit has some loads wired in series and some loads wired in parallel. The loads in this circuit are R1, R2, and R3. R1 is wired in series while R2 and R3 are wired in parallel.

#### What device would you use to measure electrical resistance in a circuit.

Electrical resistance is measured in ohms, and can be measured with an ohmmeter.

#### Which of the following is NOT a type of resistor?

A potentiometer is a three terminal resistor with a sliding contact. A rheostat is a two terminal variable resistor. A variable resistor is any resistor that allows you to change the amount of resistance. Potentiometers and rheostats are both types of variable resistors.

#### Which of these electrical devices can be used to store an electric charge?

Capacitors consist of one or more pairs of metal conducting plates that are separated by an insulator. The insulator is called the dielectric. An electric charge builds up when a voltage is applied across the plates, which creates an electric field.

#### What does this symbol refer to?

A transducer is any device used to convert energy from one form to another. Piezo transducers are often used in microphones where they convert sound pressure to electrical voltage.

#### The amount of energy used by a consumer in their home or business is typically measured in

A kilowatt-hour (kWh) is a unit of energy equivalent to one kilowatt (1 kW) of power expended for one hour

#### AM radio stations broadcast in which frequency range?

Frequencies are measured in kilohertz, megahertz, or gigahertz. AM radio stations broadcast in the 530-1,700 kHz range.

#### If a circuit has 8 volts of power and 4 ohms of resistance, what will the current equal?

Current is measured in amps. The formula to use here is: I = V/R I = 8/4 I = 2

#### Which of the following is the correct definition of an electrical cell?

An electrical cell supplies electrical current. Examples include batteries and solar cells.

#### What is the voltage in a circuit with 10 amps of current and 6 ohms of resistance?

The formula to use here is: V = I x R V = 10 x 6 V = 60

#### The resistor color code for 2 is

The band code for a resistor is as follows: • Black is 0 • Brown is 1 • Red is 2 • Orange is 3 • Yellow is 4 • Green is 5 • Blue is 6 • Violet is 7 • Gray is 8 • White is 9

#### What type of switch is pictured above?

Pushing the button breaks the circuit. When you release the button it returns to its normally closed (on) position.

#### Which of the following is the SI unit representing one cycle per second?

The hertz, or Hz, is the SI unit of cycles per second and is a measurement of frequency. The Ohm is a measurement of resistance and the Ampere is a measurement of flow rate of electric charge.

#### Which of the following is the most conductive element?

The most conductive material is Silver followed by Copper and Gold.

#### Which of the following statements are correct regarding a Voltmeter?

A voltmeter is used to measure the potential difference between two points. It is used in parallel with a circuit when measuring voltage. Ideally a voltmeter should have high resistance so that no current flows through it while measuring the potential difference between the two points.

#### Which of the following statements is incorrect regarding Ohm's Law?

Ohm's law states that V=IR. According to the law, voltage is directly proportional to both current and resistance while current is inversely proportional to the resistance.

#### If three different resistors are connected in parallel and a voltage is applied across them, which of the following statements is correct?

If three different resistances are connected in parallel and a voltage is applied across them then the voltage is same across all the resistances. The formula for finding power is P = VI = V(V/R) = (V^2/R). According to the formula, the resistor with the least value will have the maximum power loss and the resistor with the maximum value will have the least power loss.

#### A microwave is consuming 800 W power using a standard North American 120 V power supply. What is the approximate amount of current flowing?

The formula for finding electrical power is Power = Voltage x Currerent or P=VI. Rearranged we have I = P/V = 800/120 = 6.67 ? 7 amperes

#### Which of the following is a unit of power?

Power is the rate of doing work i.e. Power = Work/time = J/s. Electrical power is described as P=VI and the unit of power is Watt (W). Power is the product of current and voltage, so it can also be written as V.A where V represents the voltage and A represents the current.

#### Which of the following is true regarding an AC signal?

Frequency is the number of occurrences of an event per unit time. The relationship between the frequency and time period of an AC signal is f=1/T i.e. frequency is inversely proportional to the time period of an AC signal. The smaller the time period, the greater the frequency of the signal.

#### A capacitor blocks Direct Current (D.C). Hence, it is also known as a:

A blocking capacitor is also called the coupling capacitor. It is used to block the passage of flow of direct current (D.C) from one circuit to another by giving alternative passage to flow.

#### How many valence electrons are present in most semi-conductor materials?

Most semi-conductor materials have four valence electrons making them neither good conductors nor good insulators. For example, silicon and germanium are both semi-conductors and they have four electrons in their valence shells.

#### Which of the following instruments is used to measure resistance of a load?

An ohmmeter is a device which is used to measure electrical resistance. A voltmeter is a device which is used to measure voltage differences between two points in a circuit. An ammeter is a device which is used to measure electric current flowing through a circuit. A galvanometer is a more sensitive ammeter which is used to measure electric current flowing through a circuit.

#### How much current will flow through the resistor R2 if R1=R2=10 ohms and R3=20 Ohms?

The circuit in the given figure is a series ciruit. We know that the same current flows through all the resistors connected in series. The equivalent resistance of the given circuit = R1+R2+R3 = 10+10+20 = 40 ohms.

#### What does the following image represent?

The figure given represents a Rheostat. A Fixed Resistor is a resistor having a fixed or defined resistance. A variable resistor is a resistor which is used to control the current by varying the resistance. There are two types of variable resistor: rheostat and potentiometer. A rheostat has two usually two terminals (one fixed and the other moveable) while a potentiometer has three terminals (two fixed and one moveable).

#### Four bulbs are connected in a series-parallel circuit as shown in the given figure. Each bulb is exhibiting a resistance of 4 ohms. If one of two bulbs in the parallel connection blows up, then what will the effect be on the total effective resistance offered by all the bulbs?

The resistances are added in series. The equivalent resistance offered by two bulbs in parallel connection would be ((1/4)+(1/4))^-1 = 2. The effective resistance offered by all the four bulbs in this case is 4+2+4 = 10 ohms. If one of the bulbs in parallel connected blows up then the effective resistance offered by all four bulbs would be 4+4+4=12 ohms. Therefore, the effective resistance will increase.

#### A ground is not one of the following.

A ground is also called the earth in an electrical circuit. A ground is a place of lowest potential and least resistance in an electrical circuit. Ground/Earth is also a reference point in an electrical circuit from which voltages are measured and a common reference path for electric current.

#### A circuit breaker is better than a fuse because

A circuit breaker is better than a fuse because it can be reused multiple times unlike a fuse which needs to be replaced once it is blown.

#### Which of the following statements is correct?

Electron flow is the flow of electrons which actually occurs in a circuit. The electron current flows out of the negative terminal of the source through the circuit to its negative terminal. The conventional current was chosen as a convention at the time of discovery of electric currents, it assumes that the flow of current is out of the positive terminal of the source through the circuit to its negative terminal.

#### What is commonly used in a circuit in which the flow of electricity needs to pass easily in one direction but not the opposite direction?

A diode is a two terminal (i.e. anode and cathode) electrical equipment which conducts electrical current in one direction only.

#### Which of the following is not an application of a transistor?

A transistor is a semi-conductor device designed to amplify and switch electronic signals and electric power. A transistor has a wide range of applications including electric switch, amplifier, voltage and current regulator etc. A transistor is different from a transformer, a transistor is a semi-conductor device while a transformer is an electromagnetic device.

#### In a transformer

A transformer uses the properties of an inductor to transform the level of voltage in a circuit. AC flowing in wires wrapped around an iron core magnetizes the core, and in turn produces a changing magnetic field on the core. This changing magnetic field generates a voltage in a neighbouring coil of wire. Depending on the number of turns on the wire in the primary versus the secondary coil, a smaller or larger voltage can be induced in the secondary coil.

#### Which of the following statements is correct?

The operation of a motor is opposite to that of a generator. A generator converts mechanical energy into electrical energy and the motor converts electrical energy into mechanical energy.

#### Which of the following statements is correct?

Atomic number is also called the proton number. It is the number of protons present in the nucleus of any material.

#### Current I is passing through a load of resistance R. If the voltage across the load doubles and the resistance of the load is reduced by half then what is the amount of current passing through the load?

According to Ohm's law, the relationship between voltage, current and resistance is V=IR which can be rearranged as I=V/R. If the voltage doubles and the resistance is reduced by half then I1=(2V)/(0.5R)=4(V/R)=4I. Therefore, the current flowing through the load will increase four times.

#### What is the total amount of energy if a 12 C charge produces 3 V?

Voltage is defined as one joule per coulomb i.e. V=J/C ? J=VC ? J=12?3=36 J

#### Copper is a good conductor of electricity because:

Flow of electrons (electric current) is inversely proportional to the resistance. The material exhibiting the least resistance will be a good conductor of electricity. That is why copper is a good conductor of electricity.

#### A series circuit is shown in the figure. What is the voltage across resistor R3 if R1=20 ohms and R3=30 ohms?

The voltage will be divided in two resistors connected in series. The voltage across the resistor R3 is (15)(30/20+30) = 9 V

#### The electric power consumed by an electric kettle is 2000 W. If the voltage being supplied to the kettle increases 4 times and the current flowing through the kettle is decreased by half, what would be the effect on the power consumed by the kettle?

The formula of finding electrical power is P=VI. If the voltage increases 4 times and the current flowing throug the kettle becomes half then P = (4V)(1/2)I = 2(PI). The electric power of the electric kettle would become double.

#### If two different resistors are connected in series, then which of the following statements is correct regarding the electrical power consumed by the resistors?

If two resistors are connected in series then the current flowing through each resistor is the same because the current remains the same in a series. The formula of finding electrical power is P=VI. From ohms' law, we know that V=IR ? I=V/R. Putting the value of I in the formula of electrical power will give P=R(I)^2. As current is same through both resistors then electrical power is directly proportional to the resistance i.e. the bigger the resistance the higher will be the power consumed and vice versa.

#### Current flows:

Current is the flow of charges from higher potential to lower potential and current always takes the path of least resistance.

#### What would happen to the voltage if the current doubles and the resistance increases four times?

Ohm's Law states that V=IR. If current doubles and the resistance increases four times then V=(2I)(4R)=8(VI) i.e. the voltage increases 8 times.

#### A parallel combination of two resistors is connected in series with a 4 ohm resistor. If the total effective resistance by these three resistors is 10 ohms then which of the following can be the values of two resistors in parallel connection?

The resistances are added in series. The effective resistance offered by a combination of two resistors in series with a 4 ohms resistor is 10 ohms which means that the equivalent resistance of two resistances in parallel connection must be 6 ohms. Suppose one resistor is "a" ohms and the other resistor is "b" resistors then the equivalent resistance will be (ab/a+b) = 6. Therefore, 8 ohms and 24 ohms resistors will be the correct answer.

#### Which of the following statements is correct regarding inductors?

An inductor resists a change in current that is why it blocks AC. The equation of an inductor is (di)/(dt) = V/L. If you apply DC across an inductor, it will stabilize to some current flow based on the maximum current available from the current/voltage source. In this mode, the inductor presents very low resistance, so it can be said that it allows DC to pass.

#### A resistor with a 100 ohms of resistance has 10% tolerance. What does this mean?

Tolerance of a resistor indicates how much the measured value of a resistance is different from its theoretical value, and is calculated using percentages. 10% tolerance means that the resistance can be 100?10. A 100 ohms resistor with 10% tolerance may have values ranging from 90 ohms to 110 ohms.

#### Rectification is an important application of a diode. Rectification can be defined as:

Rectification is an important application of a diode. It is the conversion of alternating current (which reverses its direction periodically) to a direct current (which flows in only one direction).

#### What are the three terminals of a transistor?

A transistor has three connectors or terminals which are the base, the emitter and the collector. The flow of charge goes in the collector, and out of the emitter, depending on the charge flowing to the base.

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