Physical Quantities and Measurements

Answer:
A mechanical stopwatch has a dial, a seconds hand, a minutes hand and a control knob. Its dial may have 30 large divisions, each subdivided into ten parts, giving a least count of 0.1 s. Pressing the knob starts, stops and resets the watch. A digital stopwatch displays time electronically and commonly measures to 0.01 s. Stopwatches are used to measure the duration of laboratory events, but human reaction time can affect readings.

Answer:
A measuring cylinder is a graduated transparent container marked in millilitres or cubic centimetres. It measures liquid volume and the volume of some solids. Place it on a horizontal surface and keep the eye level with the liquid surface. Water forms a concave meniscus and its reading is taken at the bottom. Mercury forms a convex meniscus and its reading is taken at the top. Viewing from above or below causes parallax error.

Answer:
Choose a liquid in which the solid does not dissolve. Pour the liquid into a measuring cylinder and record its initial volume at the correct meniscus level. Immerse the solid completely without splashing and record the final volume. The rise in liquid level is caused by displacement. Volume of solid = final volume - initial volume. Since 1 mL equals 1 cm³, the result may be expressed in either unit.

Answer:
Place the displacement can on a horizontal surface and fill it until water stops dripping from the spout. Put a beaker under the spout. Tie the solid with a thread and lower it completely into the water. The solid displaces water, which flows into the beaker. Measure the collected water with a measuring cylinder. The volume of the displaced water is equal to the volume of the immersed solid.

Answer:
Human errors arise from observer limitations or incorrect procedure, such as reaction time and improper eye position. Training, careful technique and digital instruments reduce them. Systematic errors shift readings consistently because of zero error, poor calibration or incorrect markings. Calibration, comparison with an accurate instrument and correction factors reduce them. Random errors produce unpredictable variations due to environmental changes such as temperature, pressure or voltage fluctuations. Multiple readings and averaging reduce their effect.

Answer:
Every measurement has uncertainty because an instrument can measure only to its smallest calibrated division. For an analogue instrument, the maximum uncertainty is commonly taken as half the least count. For example, a ruler with a least count of 0.1 cm may give a conventional uncertainty of +/-0.05 cm. Uncertainty can be reduced by using a more precise instrument, repeating measurements, measuring several identical items together and calculating an average.

Answer:
Significant figures include all digits known with certainty plus the first estimated or doubtful digit. All non-zero digits are significant. A zero between non-zero digits is significant, as in 5.06. Leading zeros are not significant, as in 0.0034. Trailing zeros to the right of a decimal are significant, as in 2.40. In scientific notation, all digits in the coefficient are significant. Significant figures communicate the precision and uncertainty of a measurement.

Answer:
Precision describes how closely repeated measurements agree with one another. Accuracy describes how close a measurement is to the accepted or true value. Measurements may be precise but inaccurate if they are closely grouped around a wrong value, often because of systematic error. They may be accurate on average but not precise if readings are widely scattered. The best measurements are both precise and accurate: repeated values are close together and close to the accepted value.