AQA A Level Physics复习笔记5.3.1 Resistors in Series & Parallel

The combined resistance R in the following series circuit is 60 Ω.What is the resistance value of R2?A.     100 Ω               B.     30 Ω               C.     20 Ω               D.     40 Ω

The most common mistake in questions about parallel resistors is to forget to find the reciprocal of RT (1/RT) instead of RT. Here is a maths tip to rejig your memory on reciprocals:

• The reciprocal of a value is 1 / value
• For example, the reciprocal of a whole number such as 2 equals ½
  • Conversely, the reciprocal of ½ is 2

   

• If the number is already a fraction, the numerator and denominator are ‘flipped’ round

The reciprocal of a number is 1 ÷ number

• In the case of the resistance R, this becomes 1/R
• To get the value of R from 1/R, you must calculate 1 ÷ your answer
• You can also use the reciprocal button on your calculator (labelled either x-1 or 1/x, depending on your calculator)