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A student measures the thickness of a hu...

A student measures the thickness of a human hair by looking at it through a microscope of magnification 100. He makes 20 observations and finds that the average width of the hair in the field of view of the microscope is 3.5 mm. The thickness of hair is

A

0.035 mm

B

0.04 mm

C

0.35 mm

D

0.40 mm

Text Solution

Verified by Experts

The correct Answer is:
A
0.035 mm
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A student measures the thickness of a human hair by looking at it through a microscope of magnification 100. He makes 20 observations and findsd that the average width of the hair in the field of view of the microscope is 3.5mm. What is his estimate on the thickness of hair?

A boy measures the thickness of a human hair by looking at it through a microscope of magnification 100x. After 25 observations, the boy finds that the average width of the hair in the field of view of the microscope is 3.8 mm. What is the estimate on the thickness of hair?

Knowledge Check

  • A mark on a table top is seen by a student through a microscope at a distance of 30 cm from the microscope. Seeing along same vertical path he puts a slab in between microscope and table top at any position. He finds that he is to move the microscope by 5 cm, away from the salb to see the focussed image of the same mark. if refractive index of glass glass slab is 1.5. The thickness of glass slab introduced is

    A
    15 cm
    B
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    C
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    D
    20 cm

  • The alternate discs of iron and carbon, having same area of cross-section are cemented together to make a cylinder whose temperature coefficient of resistivity is zero. The change in temperature in two alternate discs is same. The ratio of their thickness and ratio of heat produced in them is found out. The resistivity of iron and carbon at 20^@C" are "1 xx 10^(-7) and 3 xx 10^(-5)Omegam and their temperature coefficient of resistance are 5 xx 10^(-3)""^(@)C and -7.5 xx 10^(-4)""^(@)C, respectively, Thermal expansion is neglected. Here, triangleR_1 +triangleR_2= 0 (where triangleR_1, and triangleR_2 , are the increase in resistances of iron and carbon, respectively, with the rise in temperature) because combined temperature coefficient of resistivity is given as zero. A copper wire is stretched to make it 1% longer. The percentage change in its resistance is Electrical resistance of certain materials, known as super conductors changes abruptly from a non zero value to zero as their temperture is lowered below a critical temperature T_c(0) An interesting property of superconductors is that their critical temperature becomes smaller than T_c(0) if they are placed in a magnetic field, that is, the critical temperature T_c(B) is a function of the magnetic field strength B. The dependence of T_c(P) on magnetic field is shown in the below figure.

    A
    0.002
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  • A student uses a metre scale, measuring upto 1 mm, to measure the length and breadth of a rectangular plate. He finds that length = 5.7 cm and breadth = 3.4 cm. What is the percentage error in the area of the plate ?

    A
    `3.5%`
    B
    `4.7%`
    C
    `5.3%`
    D
    `6.2%`

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