Understanding the Word Pair Analogy: Resistance and Ohm

The question asks us to identify a word pair that shares the same relationship as the pair 'Resistance : Ohm'. To solve this, we first need to understand the relationship between 'Resistance' and 'Ohm'.

In physics and electrical engineering, Resistance is a physical quantity that measures how much a material opposes the flow of electric current. Ohm ($\Omega$) is the SI unit used to measure electrical resistance. Therefore, the relationship between 'Resistance' and 'Ohm' is that of a Quantity and its Unit of Measurement.

We are looking for a word pair from the options where the first word is a quantity and the second word is the standard unit used to measure that quantity.

Analyzing the Options

Let's examine each option to see which one exhibits the Quantity : Unit relationship similar to Resistance : Ohm.

1. Time : Clock
   • Time is a physical quantity.
   • A clock is an instrument used to measure time.
   • The relationship here is Quantity : Measuring Instrument. This is different from Quantity : Unit. Standard units of time are seconds, minutes, hours, etc.
2. Length : Metre
   • Length is a physical quantity that describes the extent of something from end to end.
   • Metre (m) is the SI unit used to measure length.
   • The relationship here is Quantity : Unit of Measurement. This matches the relationship found in the pair 'Resistance : Ohm'.
3. Temperature : Thermometer
   • Temperature is a physical quantity that expresses the degree of hotness or coldness.
   • A thermometer is an instrument used to measure temperature.
   • The relationship here is Quantity : Measuring Instrument. This is different from Quantity : Unit. Standard units of temperature are Celsius ($^{\circ}\text{C}$), Fahrenheit ($^{\circ}\text{F}$), Kelvin (K), etc.
4. Pressure : Barometer
   • Pressure is a physical quantity defined as force per unit area.
   • A barometer is an instrument used to measure atmospheric pressure.
   • The relationship here is Quantity : Measuring Instrument. This is different from Quantity : Unit. Standard units of pressure are Pascal (Pa), Bar, psi, etc.

Conclusion

Comparing the relationships in the options with the relationship in 'Resistance : Ohm' (Quantity : Unit), we find that only the pair 'Length : Metre' follows the same pattern. Length is the quantity, and Metre is its standard unit of measurement.

Therefore, the word-pair that is related in the same way as 'Resistance : Ohm' is 'Length : Metre'.

Revision Table: Key Concepts Reviewed

Additional Information: Units and Measurement

Understanding units is fundamental in physics and other sciences. The International System of Units (SI) is the most widely used system of measurement. It defines standard units for various base quantities like length (metre), mass (kilogram), time (second), electric current (ampere), thermodynamic temperature (kelvin), amount of substance (mole), and luminous intensity (candela).

Derived units are formed by combining base units. For example, the unit for resistance, Ohm ($\Omega$), is a derived unit. Similarly, the unit for pressure, Pascal (Pa), is also a derived unit (based on force and area units).

It is important not to confuse the unit of a quantity with the instrument used to measure it. While a ruler measures length, its unit is metre or inch. While a thermometer measures temperature, its unit is Celsius or Kelvin. This distinction is crucial for solving analogy problems like the one discussed.