IT 300 Chapter 1 Problems

Impedance is made up of resistance and reactance. Choose the correct statemen

- Impedance in an AC circuit is equal to resistance plus reactance - Reactance values changes with time, while resistance does not change with time

Explain the difference between virtual connectionless and connection-oriented circuit

- In a virtual connection-oriented circuit, overhead is used to establish a communications circuit prior to the exchange of traffic. - In a connectionless circuit, no connection is made prior to communications.

Select the correct equation(s) for DC power.

- P = I^2R - P = V^2/R

Select the correct statement(s) regarding modulation

All of the above

Select the correct statement regarding EM wave

All the above

Acoustic signals are exactly the same as EM signals. As such, RF channels propagate acoustically

False

All communications systems operating within the ISM (industrial, scientific, and medical) fre-quency bands must be granted operating licenses by a regulatory agency such as the FCC prior to operations.

False

Antennas are used to transmit and receive signals. Both EM and acoustic signals can be captured by an antenna.

False

Both packet and circuit switching principles can be used in an analog network.

False

Only RF signals are considered part of the electromagnetic spectrum. Optical signals consist of photons which behave as a wave and a particle (wave-particle duality), thus optical signals are not considered part of the EM spectrum

False

Select the correct statement regarding power density

For an unguided signal, power density decreases as it travels away from the transmitter

What is true regarding Ohm's Law?

Given a 10 Ω resistive load, as voltage increases, current increases

Describe the difference between a DC (direct current) and AC (alternating current) circuit.

In a DC circuit, voltage remains constant as does the direction of current. The voltage in AC circuits changes with time between positive and negative values, resulting in changes in the direction of current within the circuit.

Describe the difference between impedance and resistance.

Resistance opposes the flow of current. In a DC circuit, only resistance is expe-rienced. However, in an AC circuit where voltage and current directions change over time, a time varying reactive compo-nent accompanies the resistive component within the circuit. Impedance is the com-bination of resistance and the time vary-ing component of reactance.

FM broadcast radio is an example of

Simplex communications

What is the purpose of a transducer?

They transform one type of energy into another type of energy (e.g., acoustic signals into electrical signals and vice versa)

Select the correct statement regarding acoustic and electrical signals

Transducers are required to turn acoustic signals into an electrical signal

An EM wave consists of an electrical wave and a magnetic wave separated by 90°. An EM wave is created when current travels through a conductive wire.

True

If both voltage and current waveforms have the same phase angles, they are in-phase to one another and the transfer of power from the source to the load is highly efficient.

True

In the transmission line model, time varying periodic and aperiodic signals cause voltage and current phase angles to change over time leading to the creation of reactive elements that reduce real power.

True

Power factor (PF) can be determined for any DC or AC circuit.

True

Power in watts is related to voltage, resistance, and current

True

Push-to-talk radios (e.g., CB radios), operate in half-duplex mode.

True

RF signals propagate as an EM wave. Optical signals behave as both a wave and a particle as it propagates. Although optical waves possess this "wave-particle duality," they are still consid-ered EM waves.

True

Regarding an ideal isotropic antenna, the transmitted power spreads over the surface area of a sphere with the sphere's radius equal to the distance measured from the transmit antenna.

True

The purpose of modulating a signal is to move the baseband signal to a higher position in the frequency spectrum by mixing it with a carrier waveform.

True

When using the frequency-division multiplexing (FDM) method, guard bands must be placed in-between frequency channels to prevent adjacent channel interference.

True

Which if the following describes the relationship between current (I), voltage(V), and resistance (R)

V = IR

What is a virtual circuit?

Virtual circuits are shared physical circuit

Select the correct statement(s) regarding DC and AC circuits.

Voltage and current levels change with time in an AC circuit

_______ describes the electrical charge stored between parallel plates of opposite voltage polarity.

Capacitance

Explain how capacitive and inductive reactance effects impedance over time

Capacitance and inductance are both time varying elements that make up reactance and therefore decrease the real component of resistance. However, capacitance and inductance have opposite effects upon one another and can be used to reduce or eliminate the reactance in an AC power circuit.