Physics 9702 · AS & A Level
Characteristics of alternating currents
100 practice questions on Characteristics of alternating currents, with worked solutions and instant marking.
A digital signal is created by taking samples from an analogue signal and then sending those samples through an analogue-to-digital converter (ADC).
Feb/March 2016
State two consequences of negative feedback on the gain of an amplifier that uses an operational amplifier (op-amp).
Feb/March 2016
State three advantages that an optic fibre has over a metal wire when carrying a signal.
Feb/March 2017
Fig. 6.1 can be used as a block diagram to show the digital transmission of speech.
Feb/March 2018
An ideal operational amplifier (op-amp) would have a voltage gain that remains constant and an infinite slew rate.
Feb/March 2019
The output from a power supply can be written as $V = 9.0 \sin 20t$, with $V$ denoting potential difference in volts and $t$ representing time in seconds.
Feb/March 2020
State the meaning of amplitude modulation (AM) of a radio wave.
Feb/March 2021
Many radio stations are now transmitted on FM instead of AM. In general, FM uses much higher frequencies for broadcasting than AM.
May/June 2010
A communications satellite orbiting Earth, shown in Fig. 12.1, is sent a $14\,\text{GHz}$ signal from a ground station on Earth with power $18\,\text{kW}$. The signal power loss between the ground station and the satellite is $190\,\text{dB}$.
May/June 2010
An optic fibre is to be used to provide a telephone link between two towns. The distance between the towns along the optic fibre is $75\,\text{km}$.
May/June 2010
What does the root-mean-square (r.m.s.) value of an alternating voltage mean?
May/June 2010
Negative feedback can be employed in amplifier circuits.
May/June 2010
A telephone connection between two towns is to be supplied by means of an optic fibre. The optic fibre stretching between the two towns has a length of $75\,\text{km}$.
May/June 2010
Explain what is meant by the root-mean-square (r.m.s.) value of an alternating voltage.
May/June 2010
Negative feedback can be used in amplifier circuits. State what is meant by negative feedback.
May/June 2010
Describe what frequency modulation (FM) means.
May/June 2011
Many television receivers are linked to an aerial by a coaxial cable, and Fig. 12.1 shows this type of cable.
May/June 2011
Long-distance radio communication using ionospheric reflection has, to a large extent, been superseded by satellite communication.
May/June 2011
As shown in Fig. 6.1, an alternating current supply is connected in series with a resistor $R$. The current $I$ in the resistor, measured in amps, changes with time $t$ (measured in seconds) according to $I = 9.9\sin(380t)$.
May/June 2011
For long-distance communication, the reflection of radio waves by the ionosphere has largely been superseded by satellite communication.
May/June 2011
An alternating current supply is connected in series with resistor R, as shown in Fig. 6.1. The current I in the resistor, with time t measured in seconds and I measured in amps, varies according to the expression I = 9.9\sin(380t).
May/June 2011
In a mobile phone system, the system coverage is broken up into a number of cells.
May/June 2012
A signal sent across a long distance will be attenuated, and it will also collect noise.
May/June 2012
Fig. 12.1 shows an incomplete simplified block diagram of the circuitry in a mobile-phone handset.
May/June 2012
Within a mobile phone system, the region covered by the system is broken up into several cells. For this system, Explain why
May/June 2012
A radio station broadcasts music by means of an amplitude-modulated wave.
May/June 2013
An optic fibre is employed to carry digital telephone signals. The power fed into the optic fibre is $9.8\,\text{mW}$. The effective noise level in the receiver circuit is $0.36\,\mu\text{W}$, as shown in Fig. 12.1. The signal-to-noise ratio at the receiver must stay at or above $28\,\text{dB}$. For this transmission with no repeater amplifiers, the greatest possible length of the optic fibre is $85\,\text{km}$.
May/June 2013
The digital transmission of speech can be shown by the block diagram in Fig. 12.1.
May/June 2013
A radio station sends out an amplitude-modulated wave to carry music.
May/June 2013
An optic fibre carries digital telephone signals. The input power to the optic fibre is $9.8\,\text{mW}$. As shown in Fig. 12.1, the effective noise level in the receiver circuit is $0.36\,\mu\text{W}$. The signal-to-noise ratio at the receiver must stay at or above $28\,\text{dB}$. If no repeater amplifiers are used for this transmission, the greatest possible length of the optic fibre is $85\,\text{km}$.
May/June 2013
A microphone signal is to be sent in digital form, and Fig. 13.1 shows a block diagram of part of the transmission system.
May/June 2014
State the meaning of attenuation in a signal.
May/June 2014
The output from a microphone is to be sent as a digital signal. Figure 13.1 shows a block diagram of part of the transmission system.
May/June 2014
State what is meant by the attenuation of a signal.
May/June 2014
Information can be transmitted through several different communication channels.
May/June 2015
Within many systems for distributing electrical energy, the energy is transmitted by alternating current at high voltages.
May/June 2015
One way to communicate is through the use of a coaxial cable. This cable is shown in Fig. 11.1.
May/June 2015
At its most basic level, a mobile phone handset is a radio transmitter and receiver.
May/June 2015
Information can be sent through different communication channels. Name one example, in each case, of a device where information reaches the device by means of
May/June 2015
In many electrical-energy distribution systems, transmission is carried out with alternating current at high voltages.
May/June 2015
The way the sinusoidal current $I$ varies with time $t$ in a resistor of resistance $450\,\Omega$ is shown in Fig. 11.1. Use the information in Fig. 11.1 to determine, over the interval from $t = 0$ to $t = 30\,\text{ms}$.
May/June 2016
The change in the voltage level of part of an analogue signal with respect to time $t$ is illustrated in Fig. 5.1. The signal is sampled every $0.25\,\text{ms}$. Each sample is turned into a four-bit digital number. Fig. 5.2 shows several times $t$ at which the voltage level is sampled. The digital number for $t = 0$ is shown.
May/June 2016
A radio station's signal is amplitude modulated.
May/June 2016
An ideal operational amplifier (op-amp) possesses infinite voltage gain together with infinite slew rate.
May/June 2016
The sinusoidal current I in a resistor of resistance 450\,\Omega varies with time t as shown in Fig. 11.1. From Fig. 11.1, determine, for t = 0 to t = 30\,\text{ms},
May/June 2016
Fig. 5.1 shows how the voltage level of part of an analogue signal changes as time $t$ passes. Sampling is carried out at $0.25\,\text{ms}$ intervals, and each sample is then turned into a four-bit digital number. Fig. 5.2 gives several values of time $t$ at which the voltage level is sampled. The digital number at time $t = 0$ is shown.
May/June 2016
The inverting-amplifier circuit that uses an ideal operational amplifier (op-amp) is illustrated in Fig. 8.1.
May/June 2016
Fig. 3.1 may be used to illustrate how speech is transmitted digitally with the block diagram.
May/June 2017
State two advantages of sending data in digital form rather than analogue form.
May/June 2017
Fig. 3.1 provides a block diagram that illustrates digital transmission of speech.
May/June 2017
In radio communication, the bandwidth of an FM transmission is larger than the bandwidth of an AM transmission.
May/June 2018
Amplifiers often make use of negative feedback.
May/June 2018
As a signal is transmitted, it suffers attenuation and also picks up noise.
May/June 2019
For a signal sent through an optic fibre:
May/June 2019
As a signal is transmitted, it experiences attenuation and picks up noise.
May/June 2019
Using optic fibres to send signals has, for the most part, taken over from coaxial cables. Their benefits include a larger bandwidth and far less crosstalking.
May/June 2020
A microphone’s output is fed through a non-inverting amplifier, which contains an operational amplifier (op-amp).
May/June 2020
Telephone signals can be sent either through an optic fibre or through a wire pair.
May/June 2020
An ideal operational amplifier (op-amp) is linked to a load resistor. The op-amp is taken to have infinite bandwidth and zero output resistance.
May/June 2020
For signal transmission, optic fibres have largely superseded coaxial cables. Their benefits include a wider bandwidth and far less crosstalking.
May/June 2020
The signal coming from a microphone is handled by a non-inverting amplifier. This amplifier contains an operational amplifier (op-amp).
May/June 2020
State what the term amplitude modulation (AM) of a radio wave means.
May/June 2021
Using heating effect as the reference, explain what is meant by the root-mean-square (r.m.s.) value of an alternating current.
May/June 2021
A carrier wave with sinusoidal form keeps a constant amplitude and has a frequency of $1.2\,\text{MHz}$. It is then modulated by a signal wave so that a $1.0\,\text{V}$ displacement in the signal wave produces a $25\,\text{kHz}$ shift in frequency. The signal wave has frequency $8.0\,\text{kHz}$ and amplitude $2.0\,\text{V}$.
May/June 2021
State what the term infinite input impedance means.
May/June 2021
State the meaning of amplitude modulation (AM) of a radio wave.
May/June 2021
The circuit includes a power supply that supplies a sinusoidal alternating input voltage $V_{\text{IN}}$. An output voltage $V_{\text{OUT}}$ is taken across a load resistor $R$, as illustrated in Fig. 7.1.
May/June 2024
A power supply in the circuit provides a sinusoidal alternating input voltage $V_{\text{IN}}$. An output voltage $V_{\text{OUT}}$ appears across a load resistor $R$, as illustrated in Fig. 7.1.
May/June 2024
Wire pairs are one communication method, although they suffer from substantial noise and attenuation.
Oct/Nov 2010
Fig. 9.1 shows an amplifier circuit that uses an operational amplifier (op-amp).
Oct/Nov 2010
Wire pairs are one method of communication, but they suffer from high noise levels and attenuation.
Oct/Nov 2010
Fig. 9.1 shows an amplifier circuit that uses an operational amplifier (op-amp).
Oct/Nov 2010
Data can be carried either by an analogue signal or by a digital signal.
Oct/Nov 2010
The current $I$ in a resistor varies with time $t$ as shown in Fig. 6.1. This current-time change is sinusoidal.
Oct/Nov 2010
Fig. 11.1 shows a simplified block diagram of a mobile phone handset.
Oct/Nov 2011
How $V$ changes with time $t$ for an alternating voltage supply of frequency $50\,\text{Hz}$ is plotted in Fig. 6.1.
Oct/Nov 2011
Section B. Answer every question in the spaces provided.
Oct/Nov 2011
Fig. 11.1 presents a simplified block diagram of a mobile phone handset.
Oct/Nov 2011
Fig. 6.1 shows how the output V of an alternating voltage supply with frequency 50\,\text{Hz} varies as time t passes.
Oct/Nov 2011
Part B
Oct/Nov 2011
In a cellular phone network, a region is split into several cells, and each cell has its own base station.
Oct/Nov 2011
In present-day communication systems, most data is sent in digital form instead of analogue form. Suggest three advantages of transmitting data in digital form.
Oct/Nov 2012
Wire pairs used to carry telephone signals are susceptible to cross-linking.
Oct/Nov 2012
In present-day communications systems, most data is sent in digital rather than analogue form. Suggest three advantages of transmitting data in digital form.
Oct/Nov 2012
In commercial radio, audio signals are carried by carrier waves after those carrier waves have been modulated.
Oct/Nov 2012
Suggest one application in which signals are transmitted through a wire pair.
Oct/Nov 2012
The way the output $V$ from a microphone changes with time $t$ is shown in Fig. 11.1. A four-bit analogue-to-digital converter (ADC) processes the output and samples it at intervals of $0.25\,\text{ms}$. The first sample is taken at $t = 0$ and appears in Fig. 11.2.
Oct/Nov 2013
Suggest why attenuation of a signal in channels of communication is normally measured on a logarithmic scale instead of a linear one.
Oct/Nov 2013
The way the output $V$ from a microphone changes with time $t$ is shown in Fig. 11.1. A four-bit analogue-to-digital converter (ADC) processes the output by taking a sample every $0.25\,\text{ms}$. The first sample is taken at $t = 0$ and is shown in Fig. 11.2.
Oct/Nov 2013
Suggest why attenuation of a signal in channels of communication is normally measured on a logarithmic scale rather than a linear one.
Oct/Nov 2013
Data can be sent either in analogue form or in digital form.
Oct/Nov 2013
State two reasons why frequencies in the gigahertz (GHz) range are used for satellite communication.
Oct/Nov 2013
State any three properties of an ideal operational amplifier (op-amp).
Oct/Nov 2013
Information can be sent along a range of communication channels.
Oct/Nov 2014
An alternating current has a mean value of zero.
Oct/Nov 2014
Information can be transferred through different communication channels. State one application, for each case, in which information is transferred by microwaves.
Oct/Nov 2014
The average value of an alternating current is zero.
Oct/Nov 2014
Distinguish an analogue signal from a digital signal.
Oct/Nov 2014
In a mobile phone system, the country is split into several cells, and each cell has its own base station.
Oct/Nov 2014
The carrier wave undergoes frequency modulation.
Oct/Nov 2015