Kilohertz (kHz) is a unit commonly used in electronics and communication to measure which physical quantity?

Introduction / Context:
Modern electronic and communication systems rely heavily on signals that vary with time. The rate at which these signals repeat is described by their frequency. Units such as hertz, kilohertz, megahertz, and gigahertz are widely used to specify operating ranges of radio stations, microprocessors, and communication links. This question asks what physical quantity is measured in kilohertz (kHz).

Given Data / Assumptions:

• Kilohertz is written as kHz, where kilo indicates one thousand.
• We are dealing with electromagnetic and radio wave applications.
• Options include electromagnetic radio wave frequencies, resistance, power for one ampere, and voltage.
• We assume SI based definitions of electrical and wave quantities.

Concept / Approach:
The hertz (Hz) is the SI unit of frequency and is defined as one cycle per second. Kilohertz is one thousand hertz, meaning one thousand cycles per second. Frequency describes how many times a periodic phenomenon repeats every second. In radio and communication engineering, frequency in kilohertz or megahertz is used to label radio stations, carrier signals, and clock signals. Electric resistance is measured in ohms, power in watts, and voltage in volts, not in kilohertz.

Step-by-Step Solution:
Step 1: Recognise that the base unit hertz (Hz) measures frequency, which is number of cycles per second. Step 2: Understand that kilohertz (kHz) means one thousand hertz, so 1 kHz = 1000 Hz. Step 3: In radio and electromagnetic applications, broadcast bands are labelled, for example, as 1000 kHz or 100 MHz, indicating how many times the electromagnetic field oscillates each second. Step 4: Electric resistance is measured in ohms (symbol ohm), power is measured in watts (W), and voltage is measured in volts (V); none of these use kilohertz as their unit. Step 5: Therefore, kilohertz is a unit that measures electromagnetic and radio wave frequencies, that is, frequency of periodic signals.

Verification / Alternative check:
When tuning an AM radio, station frequencies are often displayed in kilohertz, such as 810 kHz or 1200 kHz. When examining a microcontroller data sheet, the clock speed may be given in kilohertz or megahertz, for example 16 MHz, which is 16000 kHz. In both cases, the quantity described is how many cycles occur each second. Ohm, watt, and volt appear elsewhere in such data sheets associated with resistance, power rating, and supply voltage, confirming the different roles of these units.

Why Other Options Are Wrong:
Electric resistance: Measured in ohms, representing opposition to current flow, not in kilohertz. Power used by a current of one ampere: Power is measured in watts and involves both current and voltage, not frequency units. Electric potential difference (voltage): Measured in volts; it can be associated with alternating signals that have a frequency, but the unit kilohertz applies to the rate of variation, not to the voltage itself.

Common Pitfalls:
Students may confuse frequency with speed or think that kilohertz measures how strong a signal is. It is important to remember that frequency only tells how often a signal repeats, not how large it is. Another common confusion is mixing units seen together in circuit descriptions. For example, a waveform may be described as 5 V amplitude at 1 kHz, but here volt refers to amplitude and kilohertz to repetition rate. Keeping these distinct helps avoid mistakes.

Final Answer:
Kilohertz (kHz) is a unit that measures electromagnetic and radio wave frequencies, that is, frequency in thousands of cycles per second.