The focal length of a concave mirror is 20 cm. An object is placed at 30 cm from the mirror. The image distance is: MCQ with Answer and Explanation
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Question #1
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A physical quantity is measured as 12.345 ± 0.005 units. The relative error in this measurement is approximately:
Correct Answer: Option B
Explanation:
Relative error = (Absolute error) / (Measured value) = 0.005 / 12.345 ≈ 0.000405. Converting to percentage: 0.000405 × 100% ≈ 0.0405% ≈ 0.04%. Relative error quantifies precision independent of measurement scale. Absolute error (±0.005) indicates instrument precision. This concept is vital for comparing measurement reliability across different magnitudes. Memory tip: Percentage error = (Absolute error / True value) × 100. Competitive exams often test this calculation with varying significant figures to assess numerical proficiency.
Relative error = (Absolute error) / (Measured value) = 0.005 / 12.345 ≈ 0.000405. Converting to percentage: 0.000405 × 100% ≈ 0.0405% ≈ 0.04%. Relative error quantifies precision independent of measurement scale. Absolute error (±0.005) indicates instrument precision. This concept is vital for comparing measurement reliability across different magnitudes. Memory tip: Percentage error = (Absolute error / True value) × 100. Competitive exams often test this calculation with varying significant figures to assess numerical proficiency.
Question #2
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A wave of frequency 500 Hz has speed 350 m/s. Wavelength is
Question #3
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A body moves with uniform acceleration. The graph between velocity and time is:
Correct Answer: Option C
Explanation:
Uniform acceleration means constant rate of change of velocity: a = dv/dt = constant. Thus v = u + at, a linear equation in t. Graph is straight line with slope = acceleration. Parallel to time axis (A) implies zero acceleration (constant velocity). Parabola (C) is for position-time under constant acceleration. Memory tip: 'v-t graph slope = acceleration; area = displacement'. This graph interpretation question tests kinematics fundamentals, frequently examined in competitive exams. Always link graph features to physical quantities: slope, area, intercepts have specific meanings in motion graphs.
Uniform acceleration means constant rate of change of velocity: a = dv/dt = constant. Thus v = u + at, a linear equation in t. Graph is straight line with slope = acceleration. Parallel to time axis (A) implies zero acceleration (constant velocity). Parabola (C) is for position-time under constant acceleration. Memory tip: 'v-t graph slope = acceleration; area = displacement'. This graph interpretation question tests kinematics fundamentals, frequently examined in competitive exams. Always link graph features to physical quantities: slope, area, intercepts have specific meanings in motion graphs.
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