Quiz: Mechanical Engineering

Exam: UPPSC AE/Lecturer

Topic: Gears

Each question carries 3 marks

Negative marking: 1 mark

Time: 8 Minutes

Q1. Efficiency in a normal spur gear pair will be-

(a) above 98%

(b) To – 80%

(c) less than 50%

(d) less than 30%

Q2. The ratio of base circle radius and pitch circle radius in an involute gear is equal to:

(a) Sin ϕ

(b) Cos ϕ

(c) tan ϕ

(d) Cosec ϕ

Q3. Which of the following statements regarding ‘Mitre gears’ is correct? These are employed for______________________

(a) great speed reduction

(b) minimum axial thrust

(c) equal speed

(d) minimum back-lash

Q4. Which one of the following is true for involute gears?

(a) Interference is inherently absent

(b) Variation in center distance of shaft increases radial force

(c) A convex flank is always in contact with concave flank

(d) Pressure angle is constant throughout the teeth engagement

Q5. In the case of an involute toothed gear, involute starts from

(a) Addendum circle

(b) Dedendum circle

(c) Pitch circle

(d) Base circle

Q6. Which one of the following options is correct to describe the speed ratio of a simple gear train?

(a) N_1/N_2 = T_1/T_2

(b) N_1/N_2 = T_2/T_1

(c) N_1/N_2 = √(T_2/T_1 )

(d) N_1/N_2 = √(T_1/〖T 〗_2 )

Where-

N1 = Revolutions per minute of driving gear

N2 = Revolution per minute of driven gear

T1 = Number of teeth on driving gear

T2 = number of teeth on driven gear

Solutions

S1. Ans.(a)

Sol. efficiency of spur gear is about 98%.

S2. Ans.(b)

Sol. we know that for an involute gear

Base circle dia. = pitch circle dia. X cosϕ

Hence, cosϕ = (Base circle dia.)/(pitch circle dia.)

ϕ→ Pressure angle

S3. Ans.(c)

Sol. Bevel gears with equal size and shaft at 90° are called mitre gears. Which causes equal speed of input and output shafts.

S4. Ans.(d)

Sol. in involute gear pressure angle does not vary with motion of the gears. But in cycloidal gears, pressure angle changes with motion.

Interference can occur in involute gears due to discrepancy in profile of gears.

Variation in center distance decrease or increase radial force.

S5. Ans.(d)

Sol. Involute profile starts from base circle. Below base circle profile of gear is non-involute.

S6. Ans.(b)

Sol. for a simple gear train speed ratio can be defined as

Noriver/Noriven=N_1/N_2 = T_2/T_1

T_1= No. of teeth on gear 1 or driver gear

T_2= No. of teeth on gear 2 or driven gear