NDA (II) 2019 General Ability Test · Question 98 of 148

Correct — A, 318 K. Convert in two steps. First Fahrenheit to Celsius: C = (F - 32) x 5/9 = (113 - 32) x 5/9 = 81 x 5/9 = 45 C. Then Celsius to Kelvin: K = C + 273 = 45 + 273 = 318 K.

• (b)45 K — 45 is the temperature in degrees Celsius, not in Kelvin. You must still add 273 to reach the Kelvin value (45 + 273 = 318 K).
• (c)62.8 K — This results from a faulty conversion. Carrying out the correct two steps (F to C, then C to K) gives 318 K.
• (d)335.8 K — This looks like adding 273 to a mis-converted Celsius figure. The correct Celsius value is 45 C, which gives 318 K, not 335.8 K.

Temperature can be expressed on the Fahrenheit, Celsius and Kelvin scales. To go from Fahrenheit to Kelvin you first convert to Celsius using C = (F - 32) x 5/9, then to Kelvin using K = C + 273. The Kelvin (SI) scale starts at absolute zero and shares the same degree size as Celsius.

This is a two-step conversion and the common error is stopping after one step. Convert 113 F to Celsius (45 C), then remember to add 273 to reach Kelvin (318 K). Option (b) is the trap for anyone who forgets the second step.

• C = (F - 32) x 5/9; F = (C x 9/5) + 32.
• K = C + 273.15 (about 273 for exam purposes).
• 113 F = 45 C = 318 K.
• 0 K is absolute zero; the Kelvin and Celsius degree are the same size.

• Forgetting the second step (adding 273) and stopping at 45.
• Adding 273 before converting to Celsius, or swapping 5/9 and 9/5.

Scale-conversion sums give a value on one scale and ask for another - apply Fahrenheit to Celsius to Kelvin in order.

No directly related past PYQ was found.

• practice — not a real PYQ

  The boiling point of water is 100 C. On the Kelvin scale this is

  • (a)273 K
  • (b)373 K
  • (c)100 K
  • (d)173 K

  Answer(b) 373 K - add 273 to 100.

• practice — not a real PYQ

  A temperature of 50 C expressed in Fahrenheit is

  • (a)122 F
  • (b)90 F
  • (c)82 F
  • (d)132 F

  Answer(a) 122 F - (50 x 9/5) + 32.