Measurement Book Back Questions 8th Science Lesson 1
8th Science Lesson 1
1] Measurement
Book Back Questions with Answer and Do You Know Box Content
Do You Know?
The ‘CGS’, ‘MKS’ and SI units are metric systems of units and ‘FPS’ is not a metric system. It is a British system of units.
In December, 1998, the National Aeronautics and Space Administration (NASA), USA, launched the Mars Climate Orbiter to collect data about the Martian climate. Nine months later, on September 23, 1999, the Orbiter disappeared while approaching Mars at an unexpected low altitude. An investigation revealed that the orbital calculations were incorrect due to an error in the transfer of information between the spacecraft’s team in Colorado and the mission navigation team in California. One team was using the English FPS system of units for calculation, while the order team was using the MKS system of units. This misunderstanding caused a loss of 125 million dollars approximately.
Problem 1:
If 2 coulomb of charge flows through a circuit for 10 seconds, calculate the current.
Solution: Charge (Q) = 2 C
Time (t) = 10 s
I = Q/t = 2/10 = 0.2 A.
Luminous flux or Luminous power is the measure of the perceived power of light. Its SI unit is ‘lumen’. One lumen is defined as the luminous flux of the light produced by the light produced by the light source that emits one candela of luminous intensity over a solid angle of one steradian.
The number 6.023 x 1023 is also known as Avogadro number.
Problem 2: Convert 60o into radian.
Solution: We know that, 1o = π/180
60o = π/180 x 60 = π/3 radian.
Problem 3: Convert π/4 into degrees.
Solution: We know that, π radian = 180o
π/4 radian = 180/4 = 45o.
Until 1995, plane angle and solid angle were classified under supplementary quantities. In 1995, they were shifted to derived quantities.
Greenwich Mean Time (GMT) is the mean solar time at the Royal Observatory, located at Greenwich in London. It is measured at the longitude of zero degree. The Earth is divided into 24 zones, each of a width of 15 degree longitude. These regions are called as “Time Zones”. Time difference between two adjacent time zones is 1 hour.
Indian Standard Time (IST) : The location of Mirzapur in Uttar Pradesh is taken as the reference longitude of the Indian Standard Time. It is located at 82.5 degree longitude. IST = GMT + 5:30 hours.
Problem 5: Round off the number 1.868 to two decimal places.
Solution: We need to round off the number to two decimal places. So, the last digit to be kept is 6. Since the next digit is more than 5, we should increase the second digit by one. So, the answer is 1.87.
Choose the best answers:
1. Which one the following systems of unit is the British System of unit?
(a) CGS
(b) MKS
(c) FPS
(d) SI
2. Electric current is a ____________ quantity.
(a) Base
(b) Supplementary
(c) Derived
(d) Professional
3. SI unit of temperature is ____________
(a) Celsius
(b) Fahrenheit
(c) Kelvin
(d) Ampere
4. Luminous intensity is the intensity of _____________
(a) Laser light
(b) UV light
(c) Visible light
(d) IR light
5. Closeness of two or more measured values is called as _____________
(a) Accuracy
(b) precision
(c) error
(d) approximation
6. Which one of the following statement is wrong?
(a) Approximation gives accurate value.
(b) Approximation simplifies the calculation
(c) Approximation is very useful when little information is available
(d) Approximation gives the nearest value only
Fill in the blanks:
1. The solid angle is measured in ______________.
2. The coldness or hotness of a substance is expressed by _________________.
3. ______________ is used to measure electric current.
4. One mole of a substance contains __________ atoms or molecules.
5. The uncertainty in measurement is called as _____________.
6. The closeness of the measured value to the original value is _____________.
7. The intersection of two straight lines gives us ________________.
State true or false. If false, correct the statement:
1. Temperature is a measure of total kinetic energy of the particles in a system.
2. If one coulomb of charge is flowing in one minute, it is called ‘ampere’.
3. Amount of substance gives the number of particles present in a substance.
4. Intensity of light coming from a candle is approximately equal to one ‘candela’.
5. Quartz clocks are used in GPS devices.
6. Angle formed at the top of a cone is an example for ‘plane angle’.
7. The number 4.582 cam be rounded off as 4.58.
Match the following:
1. Temperature – Closeness to the actual value
2. Plane angle – Measure of hotness or coldness
3. Solid angle – Closeness to two or more measurements
4. Accuracy – Angle formed by the intersection of three or more planes
5. Precision – Angle formed by the intersection of two planes
Consider the statements given below and choose the correct option:
1. Assertion: The SI system of units is the suitable system for measurements.
Reason: The SI unit of temperature is Kelvin.
(a) Both assertion and reason are true and reason is the correct explanation of the assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) Assertion is true, but reason is false.
(d) Both assertion and reason are false.
2. Assertion: Electric current, amount of substance, luminous intensity are the fundamental physical quantities.
Reason: They are independent of each other.
(a) Both assertion and reason are true and reason is the correct explanation of the assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) Assertion is true, but reason is false.
(d) Both assertion and reason are false.
3. Assertion: Radian is the unit of solid angle.
Reason: One radian is the angle subtended at the centre of a circle by an arc of length equal to its radius.
(a) Both assertion and reason are true and reason is the correct explanation of the assertion.
(b) Both assertion and reason are true but reason is not the correct explanation of the assertion.
(c) Assertion is true, but reason is false.
(d) Both assertion and reason are false.
Answers:
Choose the best answers:
1. FPS, 2. Base, 3. Kelvin, 4. Visible light, 5. Precision 6. Approximation gives accurate value
Fill in the blanks:
1. Steradian 2. Scientists 3. Ammeter 4. 6.023 X 1023
5. Error 6. Accuracy 7. Plane angle
State true or false. If false, correct the statement:
1. False
Correct statement: Temperature is a measure of average kinetic energy of the particles in a system
2. False
Correct statement: If one coulomb of charge is flowing in one second, it is called ‘ampere’.
3. True
4. True
5. False
Correct statement: atomic clocks are used in Global Positioning System (GPS)
6. True
7. True
Match the following:
1.Temperature – Measure of hotness or coldness
2.Plane angle – Angle formed by the intersection of two planes
3.Solid angle – Angle formed by the intersection of three or more planes
4.Accuracy – Closeness to the actual value
5.Precision – Closeness to two or more measurements
Consider the statements given below and choose the correct option:
1. Both assertion and reason are true but reason is not the correct explanation of the assertion
2. Both assertion and reason are true and reason is the correct explanation of the assertion
3. Assertion is true, but reason is false
(Steradian is the unit of solid angle)