A student measures the length of a pencil as 7.50 cm. The number of significant figures is MCQ with Answer and Explanation

A student measures the length of a pencil as 7.50 cm. The number of significant figures is
A. 1
B. 3
C. 4
D. 2
Answer: Option B
Solution (By JKSSB Mock Tests)
7.50 has three significant figures (7,5,0). Trailing zero after decimal is significant. If it were 7.5 cm, two significant figures. Precision indicated by decimal places.

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Practice More Physics Questions

Question #1
Assertion (A): Fuse wire has high resistance and low melting point. Reason (R): It must melt to break circuit on overload.
A. A true, R false
B. Both A and R true, R not correct explanation
C. A false, R true
D. Both A and R true, R correct explanation

Correct Answer: Option D


Explanation:
High resistance produces more heat (I²R), low melting point ensures quick melting. Both true and R explains A.

This question belongs to: Science Physics
Question #2
The frequency of a tuning fork is 512 Hz. It produces resonance in a closed organ pipe of length 16 cm (speed of sound 340 m/s). The pipe resonates in
A. Second overtone
B. End correction needed
C. Fundamental mode
D. First overtone

Correct Answer: Option C


Explanation:
For closed pipe, fundamental f = v/(4L) = 340/(4×0.16) = 340/0.64 ≈ 531 Hz, close to 512 Hz, slight difference due to end correction. So fundamental. Approx match, SSC type.

This question belongs to: Science Physics
Question #3
A stone tied to a string is whirled in a circle. The work done by tension in string is
A. Positive
B. Variable
C. Zero
D. Negative

Correct Answer: Option C


Explanation:
Tension is towards centre, displacement is tangential (velocity). Force perpendicular to displacement, cos90°=0, work zero. Centripetal force does no work, doesn't change speed.

This question belongs to: Science Physics