Question

What is backlash error and why is it caused?
A. Backlash is the error in motion that occurs when gears change direction
B. Backlash is the error in reading that occurs due to least count of the instrument
C. Backlash is the error in reading that occurs due to zero error of instrument
D. None of the above

Answer 1

Hint: Backlash error is very common in instruments like screw gauge, spherometer, etc. Backlash error sometimes called play or lash (by mechanical engineers) is generally encountered when we try to move the instrument back and forth rapidly i.e. when we are changing direction of motion of the instrument.

Complete answer:
Backlash error is the error that occurs while we are changing the direction of gears. We encounter backlash errors when there is a gap between the trailing face of the driving tooth and the leading face of the tooth behind the driven gear. It can be avoided by turning the gear slowly in the same direction. Backlash error can also be defined as the clearance or lost motion in a mechanism caused by gaps between the parts of the gear.
The correct answer is option A.

So, the correct answer is “Option A”.

Additional Information:
Different types of errors that are encountered while measurement.
(a) Gross error – Gross error is mostly human error. This includes an error in reading data or recording data or improper adjustment and use of instruments.
(b) Random error – It is observed that if we carefully repeat measurements of the same quantity, it shows small variation from reading to reading. There is no doubt or reason for the variation but we are not able to properly define them. Such errors are called random errors.
(c) Systematic error – During experimenting certain sources of error operate constantly or systematically making the readings systematically smaller or greater than the correct reading. These errors are called systematic error.

Note:
As already mentioned this type of error may be avoided by carefully rotating the instrument in the same direction slowly. Theoretically, there should be no zero error (ideal case). However, some backlash must be provided to avoid jamming. Some reasons for the presence of backlash is a manufacturing defect, thermal expansion, lubrication, etc.