= p (length of 1 division on main scale – length of 1 division on vernier scale) = p × L.C. Thus the actual length of the rod is 1.2 cm plus the length ab (i.e., the length between the 1.2 cm mark on the main scale and 0 mark on vernier scale). of a screw gauge is the distance moved by it in rotating the circular scale by one division. L.C. The units of quantities other than those measured in fundamental units can be obtained in terms of the fundamental units, and thus the units so obtained are called derived units. The rachet is provided to avoid excessive pressure on the wire. Hence, a vernier callipers can measure length correct up to 0.01 cm. SELINA Solutions for Class 9 Physics Chapter 1 - Measurements and Experimentation. Physics notes for class 9th chapter 1 PDF consist of the solved Review Questions and Conceptual Questions. From this graph, the value of acceleration due to gravity (g) can be calculated as follows. The units which are derived from the fundamental units are called derived units. of divisions on the circular scale = 100 L.C. Let T1 and T2 be the time periods of the two pendulums of lengths l1 and l2, respectively. of divisions on the vernier scale = 10 Thus, L.C. 2. = Value of 1 m.s.d./number of divisions on vernier scale = 1 mm/10 = 0.1 mm or 0.01 cm, There are 20 divisions in 1 cm on the main scale. + circular scale reading = (0.1 + 0.027) cm = 0.127 cm, (ii) Zero error = 0.005 cm Correct reading = Observed reading – zero error (with sign) = [0.127 – (+0.005)] cm = 0.122 cm, (iii) Because the zero of the circular scale lies below the base line, when the flat end of the screw is in contact with the stud, the error is positive. of vernier callipers = 0.01 cm In the shown scale, Main scale reading = 3.3 mm 6th vernier division coincides with an m.s.d. Fundamental unit: The units of the fundamental quantities are called fundamental unit.Those units which are independent cannot be derived from other unit is called fundamental unit. A pendulum with the time period of oscillation equal to two seconds is known as a seconds pendulum. To increase the accuracy, the total number of divisions on the scale must be increased. Measurement is the process of comparing a given physical quantity with a known standard quantity of the same nature. (c) The time period of oscillations of simple pendulum does not depend on the amplitude of oscillations. Then, the value of T2 is to be noted at a and b, the value of l at c and d. Then, where g is the acceleration due to gravity at that place. p = 4. (a) Vernier callipers (b) Metre scale (c) Screw gauge. = 1 mm / 100 = 0.01 mm = 0.001 cm. In 1889, one kilogramme was defined as the mass of a cylindrical piece of a platinum-iridium alloy kept at the International Bureau of Weights and Measures at serves near Paris. A vernier calipers is said to be free from zero error, if the zero mark of the vernier scale coincides with the zero mark of the main scale. It is accounted by subtracting the zero error (with sign) from the observed reading in order to get the correct reading. Zero error = +6 × L.C. of vernier callipers = 0.01 cm Main scale reading = 1.8 cm Since 4th division of the main scale coincides with the main scale, i.e. Screw gauge measures a length to a high accuracy. Then, Value of n divisions on vernier = (n – 1) x. Vernier constant is equal to the difference between the values of one main scale division and one vernier scale division. (a) 1 nanosecond = 10-9 s (b) 1 µs = 10-6 s (c) 1 mean solar day = 86400 s (d) 1 year = 3.15 × 107 s, (a) Mass (b) Distance (or length) (c) Time (d) Length, (a) ms-1 (b) kg ms-2 (c) kg m2s-2 (d) kg m-1s-2, (a) kg ms-2 (b) kg m2s-3 (c) kg m2s-2 (d) kg m-1s-2, (a) Area (b) Force (c) Energy (d) Pressure (f) Power, Wavelength of light of particular colour = 5800 Å, (a) (i) 1 Å = 10-1 nm 5800 Å = 5800 × 10-1 nm = 580 nm, (ii) 1 Å = 10-10 m 5800 Å = 5800 × 10-10 m = 5.8 × 10-7 m. (b) The order of its magnitude in metre is 10-6 m because the numerical value of 5.8 is more than 3.2. of divisions on the circular scale = 50 (i) Pitch = Distance moved ahead in one revolution = 1 mm/1 = 1 mm. Ltd. We cannot have a heavy mass having the size of a point and string having no mass. Therefore, the vernier scale reading = 4 × 0.01 cm = 0.04 cm Total reading = Main scale reading + vernier scale reading = (1.8 + 0.04) cm = 1.84 cm, (b) Observed reading = 1.84 cm Zero error = -0.02 cm Correct reading = Observed reading – Zero error (with sign) = [1.84 – (-0.02)] cm = 1.86 cm, L.C. You can download the Selina Concise Physics ICSE Solutions for Class 9 with Free PDF download option. ICSE Class 9 Physics Selina Solutions Chapter 1 – Measurement and Experimentation Physics Chapter 1 – Measurement and Experimentation topic talks about Systems of Unit and Units in SI System, Measurement of Length, Measurement of Time and Simple Pendulum. Unit is a quantity of constant magnitude which is used to measure the magnitudes of other quantities of the same manner. Examples are: Velocity – a physical quantity derived from fundamental quantities of length and time, Difference between fundamental and derived unit. If a screw moves by 1 mm in one rotation and it has 100 divisions on its circular scale, then pitch of screw = 1 mm. = + (4 × 0.01) mm = + 0.04 mm. The least count of vernier callipers is equal to the difference between the values of one main scale division and one vernier scale division. = 0.5 / 0.001 = 500. Selina Publishers Concise Physics for Class 9 ICSE Solutions all questions are solved and explained by expert teachers as per ICSE board guidelines. Exercise 1(A) Solution 1S. unit of time is second (s). 1 km = 1000 m 1 A.U. + v.s.r. Positive zero error: On bringing the two jaws together, if the zero mark of the vernier scale is on the right of the zero mark of the main scale, the error is said to be positive. The least count of an instrument is the smallest measurement that can be taken accurately with it. The main scale is graduated to read up to 1 mm and on vernier scale, the length of 10 divisions is equal to the length of 9 divisions on the main scale. 0.001 cm and zero error +0.007 cm. One lunar month is the time in which the moon completes one revolution around the earth. Its unit is hertz (Hz). of vernier divisions = 10 Zero error = +3 × L.C. = – 4 × 0.01 cm = – 0.04 cm, Correction: To get correct measurement with vernier callipers having a zero error, the zero error with its proper sign is always subtracted from the observed reading. Total length of the scale = 1 m = 100 cm No. Thus, g can be determined at a place from these measurements using the following relation: The ratio of their time periods would be 1:1 because the time period does not depend on the weight of the bob. A simple pendulum is a heavy point mass (known as bob) suspended from a rigid support by a massless and inextensible string. The time ‘t’ for 20 complete oscillations is measured with the help of a stop watch. To avoid the backlash error, while taking the measurements the screw should be rotated in one direction only. Astronomical unit (A.U.) To find this error, we note the division of the vernier scale, which coincides with any division of the main scale. If the direction of rotation of the screw needs to be changed, then it should be stopped for a while and then rotated in the reverse direction. Let n divisions on vernier callipers be of length equal to that of (n – 1) divisions on the main scale and the value of 1 main scale division be x. Measuring the length of a small rod using vernier calipers: The rod whose length is to be measured is placed in between the fixed end and the vernier scale as shown in the figure. Derived units are composed of the fundamental units and are originated from the products and ratios of the fundamental units. Correct reading = Observed reading – zero error (with sign). Solution 2S. Therefore, vernier scale reading = 6 × 0.01 cm = 0.06 cm Total reading = m.s.r. The statement ‘the distance of a star from the Earth is 8.33 light minutes’ means that the light from the star takes 8.33 minutes to reach Earth. Ratchet helps to advance the screw by turning it until the object is gently held between the stud and spindle of the screw. The zero error is of two kinds. To find this error, we note the division of the vernier scale coinciding with any division of the main scale. Measurement of diameter of wire with a screw gauge: The wire whose thickness is to be determined is placed between the anvil and spindle end, the thimble is rotated until the wire is firmly held between the anvil and spindle. Definitions of three fundamental quantities: Three systems of unit and their fundamental units: A fundamental (or basic) unit is that which is independent of any other unit or which can neither be changed nor can be related to any other fundamental unit.

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