physics notes

Understanding Measurements - Document Transcript

1. LESSON 3 Sensitivity of a measuring instrument is defined as the capability of that instrument to respond to physical Precision(consistency )and stimuli or to register small physical amount or Accuracy ,Sensitivity and Error differences. OR Introduction Sensitivity is the degree of a measuring instrument to record small change in its reading. The characteristics which are emphasized in the selection of a measuring instrument include The smallest scale division on the measuring precision , accuracy and sensitivity. instruments shows the sensitivity of the instruments. Thus the more sensitive the measuring instruments The meaning of Precision, Accuracy and the finer the scale divisions. Sensitivity. A vernier calipers is more sensitive than a ruler or Precision is the degree of uniformity or a miliammeter is more sensitive than an ammeter. A sensitive instrument is not always an accurate reproducibility of the measurements. instrument. OR Precision is the degree of a measuring Errors instrument to record consistent reading for each measurement by the same way. Any measurement of a physical quantity has errors or uncertainty. When we say the measurements are consistent, There are two types of errors. we mean that all the values of the (a) Systematic errors measurements are close together. (b) Random errors Accuracy is the degree of closeness of the Systematic errors measurements to the actual or accepted value. Systematic errors are errors in the measurement of a physical quantity due to instruments, the effects of When we say the measurements are accurate, surrounding conditions and physical constraints of the we are actually saying that the values of the observer. measurements are close to the true or The main characteristic of systematic error is that its accepeted value. magnitude is almost constant or appears in one The diagram shows the result for four shooters direction only. The value of the measurement is A, B , C and D in a tournament. Every shooters always greater or is always less than the actual value. shot five times . Sources of systematic errors are: (i) Zero errors or end errors Zero errors occurs when the instrument gives a non- zero reading when in fact the actual reading is zero. (ii) Personal error of the observer. Physical constraints or limitations of the observer can cause systematic errors. The table shows the conclusion . An example is the reaction time. Shooter Precision Accuracy (iii) Errors due to instruments The examples are; A High Low A stopwatch which is faster than normal would B Low High give readings which are always larger than the C High High actual time. D Low Low 9
2. A thermometer which is used under different Measurement Length conditions from which it was calibrated. A voltmeter manufactured in Germany had been calibarated under different temperature and We normally use ruler, measuring tape , vernier earth’s magnetic field from Malaysia where the calipers or micrometer screw gauge to measure voltmeter is used. length. (iv) Errors due to wrong assumption. Measuring Smallest scale division For example, we assumed that the value of the instrument acceleration due to gravity g is 9.81 ms-2, but the Ruler 0.1 cm or actual value may 9.79 ms-2. Hence there is a 1 mm positive error of 0.02 ms-2. Vernier 0.01cm calipers Systematic errors cannot be reduced or eliminated by Mikrometer 0.01 mm taking repeated readings using the same method, the screw gauge same instrument or by the same observer. Systematic erros can be elimated or reduced by Vernier calipers improving the procedure of taking the measurements , using a different instrument or getting somebody else to make the the measurements. For example for the zero errors can be eliminated by subtracting the zero reading from the obtained readings. Random errors The main source of random error is the observer or has non -constant size of error and is unpredictable. A pair of vernier calipers can be used to measure The characteristics of random errors are: thickness of a wire , internal and external diameter of (i) it can be positive or negative. The obtained a beaker, depths of a test tube ,etc. readings may be greater or less than the The inside jaws are used to measure internal actual value. diameters and the outside jaws are used to measure (ii) its magnitude is not constant. external diameters and thickness. Examples of random errors are: The tail is used to measure depths. (i) Parallax errors – occur when the position The main scale is marked in divisions of 0.1 cm , of the eye is not perpendicular to the scale. while the vernier scale is marked in divisions of 0.01 (ii) Different pressures are applied when cm. closing the gap of the micrometer screw gauge when it is used to measure the The following steps shows how to read the vernier diameter of a wire. calipers. • Read the main scale marking just before the (iii) Changes in the temperature during an zero marking on the vernier scale. experiment. • Find the vernier scale marking which joins (iv) Recording the wrong reading. the main scale marking. (v) Mistake in counting • The reading for a vernier scale is always recorded in cm with two decimal places To eliminate or reduce random errors , (The accuracy is 0.01 cm) repeated reading are taken. 10
3. The main scale is marked in divisions of 0.5 mm , Example 1 while the vernier scale is marked in divisions of 0.01 mm. Write down the reading of the following vernier The jaws tigh the object that is to be measured. calipers. The thimble is turned until its jaw touches the object. The ratchet knob prevents overtightening by making a click sound when the micrometer is ready to be read. The following steps shows how to read the Solution micrometer screw gauge. Read the main scale marking just before the zero marking on the vernier scale. Example 2 • Read the main scale marking just before the zero marking beforev the thimble. Based on the following diagrams write down the • Find the vernier scale marking which joins actual thickness of the objects. the main scale. • The reading for a micrometer screw gauge is always recorded in mm with two decimal places (The accuracy is 0.01 cm) Example 3 Write down the reading of the following diagrams. Solution Solution Example 4 Mikrometer screw gauge Based on the following diagrams write down the actual diameters of the objects (a) The micrometer screw gauge is used to measure thickness and diameters of very small objects. 11
4. Accuracy : …………………………………….. Reading : ……………………………………. (b) Solution Accuracy : …………………………………….. Reading : ……………………………………. Measurement Mass 12
5. Triple beam balance Accuracy : …………………………………………. Measurement Time Double-scale ammeter Accuracy of upper scale :…………………….. Mechanical stop watch Acuracy of lower scale : ………………………. Accuracy : …………………………………….. Reading :……………………………………….. Miliammeter range 0- 50 mA Electronic stop watch Accuracy:…………………………………………… Accuracy :…………………………………… Reading :………………………………………….. Reading :……………………………………. Accuracy:……………………………………… Measurement Current Measurement Temperature Ammeter range 0 – 5A Accuracy :……………………………………………. Accuracy:………………………………………….. 13
6. 5 Based on the table below, what are the measuring instruments J, K and L? Measuring instruments Measurement J 2.52 ±0.01 cm K 15.2±0.1 cm L 125.4±0.1 g J K L A Micrometer Vernier Spring screw gauge calipers balance B Micrometer Vernier Triple beam Screw gauge calipers balance C Vernier Metre Triple beam calipers ruler balance 6 Which of the following is true? TUTORIAL 3 A The parallax error is not effected to the accuracy 1 The ability of an instrument gives consistent B The accurate instrument is also the reading , when repeated readings are taken is sensitive instrument called as C The accuracy increases when the measurement nearest to actual value. A B accuracy precision C D sensitivity error 7 Which of the following is true? 2 Which of the following should be the small A A stop watch is more sensitive than an value ,so that the precision becomes high? electronic B An ammeter is more sensitive than a A B Actual value Mean galvanometer C D Relative error Relative C A vernier calipers is more sensitive deviation than a metre ruler D A thinner-walled bulb thermometer is more 3 The ability of an instrument to detect a slight sensitive than a thicker –walled bulb change that occurs in the measured quantity is thermometer called as 8 Which of the following is most likely to show a A B precision accuracy precise shooting? C D sensitivity error 4 The accuracy of an instrument increases if A the number of significant figures increases B the relative deviation relative increases C the relative error increases 14
7. D Measuring the thickness of a large number of pieces of paper to find the thickness of one piece. 13 The error is caused by the position of eye is not parallel to the scale of an instrument is called as A positive zero error B negative zero error 9 Which of the following is most likely to show an C parallax error accurate shooting but not so presicely? 14 The following table shows the readings measured by using different measuring instruments X, Y dan Z. Measuring instrument Reading / mm X 2.38 Y 52 Z 6.5 Which of the following is true? 10 It take 5.01 s for an object to move to a certain X Y Z distance. When an electronic watch is used the A Ruler Vernier calipers Mikrometer time is recorded as 4.85 s. What is the screw gauge percentage of error? B Vernier Mikrometer Measuring calipers screw gauge tape A B 0.6 % 2.1 % C Measuring Ruler Vernier C D 3.2 % 5.2 % Tape calipers E 7.7 % D Mikrometer Ruler Vernier 11 Which of the following statements about errors Screw gauge Calipers is correct? 15 Table shows readings of the thickness of a book measured by four different students. Which of A Zero error is random error the students recorded the true readings. B Random errors can be reduced by taking repeat readings. C Systematic errors can be due to Student Ruler Vernier Mikrometer instruments which are not sensitive. / cm calipers screw D Systematic errors cause the readings / cm gauge scattered on both sides of the actual /cm value. A W 2.17 2.2 2.174 B X 2.174 2.2 2.17 12 Which of the following experiment techniques C Y 2.17 2.174 2.2 can reduce systematic error of the quantity Z 2.2 2.17 2.174 D being measured? 16 Which of the following accuracy of the A Measuring the diameter of a wire at measuring instruments is true? different points along the wire. B Adjusting an ammeter to read zero before Measuring instruments Accuracy measuring a current. C Timing a large number of oscillations to A Ruler 1 mm find the period of a pendulum. B Vernier calipers 0.001 cm C Mikrometer screw gauge 0.1 mm 15
8. 17 The focal length of a convex lens is 12 cm. If the focal length is measured by using a ruler, the reading recorded ought to be A B 11.9 cm 12.0 cm C D 12.00 cm 12.1 cm 18 The diagram shows the existence of zero errors of a vernier calipers. What is the value of the zero error? A B + 0.04 cm - 0.04 cm C D + 0.06 cm - 0.06 cm The actual reading of diameter of the metal sphere is A B 2.02 cm 2.04 cm C D 2.06 cm 2.08 cm 21 The thickness of a paper is measured by using a micrometer screw gauge should be recorded as 19 The following diagram shows a vernier calipers. A 2 mm B 2.1 mm C 2.14 mm D 2.142 mm 22 Diagram shows a micrometer screw gauge. What is the reading of the vernier calipers ? Based on the diagram, what is the number of revolution of the thimble. A B 3.17 cm 3.08 cm A B 12½ 12 C C 2.18 cm 2.07 cm C D 13¾ 13 20 Figure(a) shows the existence of zero error of a 23 Diagram shows a micrometer screw gauge vernier calipers. Figure(b) shows the reading of reading when it is closed at its gap. the vernier calipers for diameter of metal sphere. 16
9. The subsequent readings must be corrected by A adding 0.02 mm B subtracting 0.02 mm C adding 0.03 mm D subtracting 0.03 mm 24 The actual reading of diameter of the metal wire is A B 8.30 mm 8.32 mm C D 8.80 mm 8.82 mm 26 A simple pendulum makes 20 complete swings in 20.35 s. Which of the following is used? A Stop watch Based on the diagram above, the thickness of a B Pendulum clock sheet of paper is C Electronic watch A B 3.25 cm 3.75 cm 27 A mass hanging from one end of a vertical C D 0.325 cm 0.0375 cm spring makes ten complete oscillations in 15 s. If the time of the oscillations is taken by a stop watch ,it should be recorded as A B 15 s 15.0 s C D 15.00 s 15.000 s 28 The figure shows a thermometer. 25 Figure(a) shows the existence of zero error of a micrometer screw gauge. Figure(b) shows the reading of the micrometer screw gauge for diameter of metal wire. What is the reading shown? 96o C 93.5o C A B 94.0 o C 94o C C D 29 Which of the following will increase the sensitivity of a mercury-in-glass thermometer/ Glass stem Capillary Size of wall tube bore A thick wide big B thin narrow big 17
10. C thick wide small Length of a pencil D thin narrow small Internal diameter of a 30 The current flows through a metal conductor is beaker between 0.01 A to 0.05 A. Which ammeter is (a) Complete the table above. most suitable to use? (b) State one reason why the diameter of the A copper wire should be measured at a few Ammeter range 0-1A different places? B Ammeter range 0-5A ………………………………………………… C Ammeter range 0-10 mA D Ammeter range 0-50 mA ………………………………………………… 31 State one precaution to be taken while What is the reading shown by the ammeter (c) above? taking measurements by using the instrument which measured the internal A B 2.4 A 2.80 A diameter of a beaker. C D 0.48 A 0.44 A ………………………………………………… 32 The function of zero adjuster in an ammeter is to ………………………………………………… A avoid zero error 34 B fasten the pointer C avoid parallax error D control the very large current 33 Measurement Measuring Accuracy (cm) Instrument Diameter of a copper wire 18
11. Diagram above shows the reading of a mikrometer screw gauge for the thickness of 5 sheets of paper. (a) What is the number of revolution of the N scale . (b) Determine the thickness of a sheet of the paper in cm. Figure(a) shows the jaws of a vernier calipers (c) Give the name and the function of M without tigh any object. Figure(b) shows the scale. jaws of the vernier calipers tigh a test tube. .................................................................... (a) What is the function of P? .................................................................... ............................................................................. .................................................................... (b) What is the smallest division on the vernier (d) State a precaution to be taken while taking scale? measurements by using the micrometer screw gauge. ............................................................................. .................................................................... (c) State the diameter of the test tube in metre. .................................................................... 36 Diagram above shows a thermometer. (a) Name component 35 (i) P ……………………………........... 19
12. .................................................................... (ii) Q ……………………………........... (ii) B (b) State the accuracy of the thermometer. …………………………………….................. .................................................................... .................................................................... (b) (c) What is the reading of the thermometer? State the accuracy of the ammeter .................................................................... .................................................................... (d) Why does the glass stem wall of the .................................................................... thermometer is thin? (c) State the reading of the ammeter. .................................................................... (e) How should you do to increase the .................................................................... accuracy of the thermometer. .................................................................... (d) State two precautions to be taken while .................................................................... taking measurements by using the ………………………………………………… ammeter. (f) Why does the thermometer use mercury? .................................................................... ………………………………………………… .................................................................... ………………………………………………… .................................................................... (g) Draw a dotted line to show the correct position of eye in the above diagram while measuring the temperature of a substance. 37 Diagram shows a miliammeter. (a) Give the name and the function of component of (i) A ........................................... …….................. 20