250+ TOP MCQs on Standard Spur Gears-1 and Answers

Machine Kinematics Multiple Choice Questions on “Standard Spur Gears – 1”.

1. Lewis equation for design of involute gear tooth predicts the dynamic load capacity of a cantilever beam of uniform strength.
a) True
b) False
Answer: b
Clarification: Lewis equation for design of involute gear tooth predicts the static load capacity of a cantilever beam of uniform strength.

2. For a pair of gears in mesh, pressure angle and module must be different to satisfy the condition of interchangeability and correct gearing.
a) True
b) False
Answer: b
Clarification: For a pair of gears in mesh, pressure angle and module must be same to satisfy the condition of interchangeability and correct gearing.

3. In skew bevel gears, the axes are
a) non-parallel and non-intersecting, and teeth are curved
b) non-parallel and non-intersecting, and teeth are straight
c) intersecting, and teeth are curved and oblique
d) intersecting, and teeth are curved and can be ground
Answer: a
Clarification: Skew bevel gears imply non-parallel, non-intersecting and curved them.

4. In case the number of teeth on two bevel gears in mesh is 30 and 60 respectively, then the pitch cone angle of the gear will be
a) tan^-12
b) п/2 + tan^-12
c) п/2 – tan^-10.5
d) tan^-10.5
Answer: d
Clarification: tanɸ = N_P/N_G
N_P = No. of teeth of pinion
N_G = No. of teeth of gear
ɸ = Pitch cone angle
ɸ = tan^-1(30/60)
ɸ = tan^-10.5.

5. Consider the following statements:
The axes of spiral bevel gear are non-parallel and intersecting.
1. The most common pressure angle for spiral bevel gear is 20^o.
2. The most common spiral angle for spiral bevel gear is 35^o.
3. Spiral bevel gears are generally interchangeable.
4. Spirals are noisy and recommended for low speeds of 10 m/s.

Which of the above statements are correct?
a) 1 and 4
b) 1 and 2
c) 2 and 3
d) 3 and 4
Answer: a
Clarification: Commonly used pressure angle is 20^o, spiral gear operation is noisy hence recommended for low speed operation.

6. Consider the following statements:
In case of helical gears, teeth are cut at an angle to the axis of rotation of the gears.
1. Helix angle introduces another ratio called axial contact ratio.
2. Transverse contact ratio is equal to axial contact ratio in helical gears.
3. Large transverse contact ratio does not allow multiple teeth to share the load.
4. Large axial contact ratio will cause larger axial force component.

Which of the above statements are correct?
a) 1 and 2
b) 2 and 3
c) 1 and 4
d) 3 and 4
Answer: c
Clarification: Transverse contact ratio may not be equal to axial contact ratio. Larger contact ratio means sharing of multiple teeth.

7. A worm gear set is designed to have pressure angle of 30⁰ which is equal to the helix angle. The efficiency of the worm gear set at an interface friction of 0.05 is
a) 87.9%
b) 77.9%
c) 67.9%
d) 57.9%
Answer: a
Clarification: ȵ = tanλ(cosɸ – μtanλ)/cosɸtanλ + μ
tanλ = -μ + √1 + μ²
tanλ = -(0.05) + √1 + (0.05)²
tanλ = 0.9512

ȵ = 89.1%

So most suitable option is ‘a’.