In our day to day life we need to measure different physical quantities. e.g.
If you want to measure distance between two end points of a line segment, you need to measure length.
If you want to know how hot an object is,you need to measure temperature.
If you want to know how fast a car is moving,you need to measure speed.
In day to day life you need to measure mass of a body,force,pressure, work, power etc. They are all physi8cal quantities.
Physical quantity-That which is to be measured is called physical quantity.
A physical quantity is a quantity that measures the properties of material or substances.
Physical quantities are of two types .
1. Fundamental quantities
2.Derived quantities
Fundamental quantities
Fundamental Quantities-
Fundamental quantities are those which can not be expressed in terms of other quantities.
A quantity which is independent of other quantities is called a fundamental quantity.
Fundamental quantities are independent to each other and can not be related to one another.
There are seven fundamental quantities
Fundamental units-
Units of fundamental quantities are called fundamental units or basic units. There are seven fundamental units.
There are seven fundamental quantities and two supplementary units.
Fundamental Quantity Fundamental Unit Symbol
1.Length meter m
2.Mass kilogram Kg
3.Time second S
4.Temperature kelvin K
5.Current ampere A
6.Amount of substance mole mol
7.Luminous Intensity candela Cd
8.Plane angle radian rad
9.Solid angle steradian sr
Derived Quantities
Derived quantity-
Derived quantity is that which can be obtained by the combination of fundamental quantities.
Physical quantity which can be obtained by multiplying, dividing OR by mathematically combining the fundamental quantities are called derived quantities.
Derived units–
Units of derived quantities are called derived units.
General conference on weights measure has approved 22 derived units.
Examples of derived quantities-
1.Weight = mass x Gravity
2.Force = Mass x Acceleration
3.Momentum = Mass x Velocity
4.Speed = Distance / Time
5.Velocity = Displacement /Time
6.Pressure= Force/Area
7.Work = Force x Displacement
8.Power = Work / Time
9.Acceleration = Velocity/Time
Derived Quantity | Derived Unit |
1.Weight = mass x Gravity | newton = kg x m/s² |
2.Force = Mass x Acceleration | newton = kg x m/s² |
3.Momentum = Mass x Velocity | Kg . m/s |
4.Speed = Distance / Time | m/s |
5. Velocity = Displacement /Time | m/s |
6. Pressure= Force/Area | pascal = N/m² |
7. Work = Force x Displacement | Joule = N x m |
8. Power = Work / Time | Watt = J/s |
9. Acceleration = Velocity/Time | m/s² = m/s ÷ s |
22 Derived quantities and their Derived units |
1.Frequency hertz(Hz) 2Force newton(N) 3. Pressure pascal(Pa) 4. Energy or work joule(J) 5. Power watt(W) 6. Electric charge coulomb(C) 7. Electric potential volt(V) 8. Electric capacitance farad(F) 9. Magnetic flux weber(Wb) 10. Magnetic flux density tesla(T) 11. Electric resistance ohm(omega) 12. Electric conductance siemens(S) 13. Inductance henry(H) 14.Temperature degree celsius 15. Plane angle radian(rad) 16. Solid angle steredian (sr) 17. Luminous flux lumen(lm) 18. Radio activity becquerel(Bq) 19. absorbed dose gray(Gy) 20. radiator dose joule/gram 21 dose equivalent sievert (Sv) 22 Catalytic activity katal(Kat) |
Scalar Quantities
Scalars are quantities that are fully described by a magnitude (or numerical value) alone.
They are quantities that have a magnitude or size, but they don’t have any direction associated with them.
Here are a few examples:
Distance: When you measure how far something is from one point to another, you’re dealing with distance. Whether you’re walking forward, backward, or sideways, the distance remains the same.
Speed: If you’re driving a car at 60 kilometers per hour, the speed is a scalar quantity because it tells you how fast you’re going, but it doesn’t specify the direction in which you’re moving.
Temperature: Whether you’re talking about a hot summer day or a chilly winter evening, temperature is a scalar quantity. It tells you how hot or cold something is without indicating any direction.
Mass: When you weigh something, you’re measuring its mass. Whether an object weighs 10 kilograms or 100 kilograms, it’s just a measure of how much stuff is there, without any direction.
Vector Quantities
Vector quantities are completely expressed by magnetude and direction both.They not only have a size or magnitude but also a direction.
Here are few examples.
Displacement: When you move from one point to another, your displacement is a vector quantity. It’s not just about how far you’ve traveled; it’s also about the direction you’ve traveled in. For example, if you move 10 meters north, your displacement is 10 meters north.
Velocity: Velocity is similar to speed, but with one crucial difference—it includes direction. So, if you’re driving a car at 60 kilometers per hour eastward, your velocity is a vector quantity because it tells you both how fast you’re going and which way you’re going.
Force: When you push or pull on an object, you’re applying a force. Like velocity, force is a vector quantity because it has both magnitude (how strong the push or pull is) and direction (which way the force is acting).
Acceleration: Acceleration is the rate at which something’s velocity is changing. If you’re speeding up or slowing down, acceleration tells you how fast that change is happening and in which direction.
Errors In Measurement Of Physical Quantity
An error may be defined as the difference between the measured and actual values.
Errors in measurement refer to the difference between the measured value and the true value of whatever it is you’re measuring. These errors can occur due to various reasons, and it’s important to understand them so we can minimize them in our experiments and calculations.
These errors can occur due to various reasons, and it’s important to understand them so we can minimize them in our experiments and calculations.
Factors which cause errors in measurement of physical quantities:
1.Limitation of instrument -Some times the instrument used for measurement is faulty. We can not get accurate measurement using faulty instrument.
2.Method of handling instruments- Some times error in measurement occur due to wrong method of handling the instrument.The user handles the instrument in wrong way.
Types of errors-
1.Systematic Errors
2.Random Errors
3. Gross Errors
Systematic Errors: These errors occur consistently and are often caused by flaws in the measuring device or the experimental setup. For example, if your ruler is slightly warped, it might always measure objects a little longer than they actually are. Systematic errors can be corrected by calibrating or adjusting the measuring instruments.
Random Errors: Unlike systematic errors, random errors occur randomly and unpredictably. They can be caused by fluctuations in environmental conditions, human error in reading instruments, or variations in the quantity being measured. For instance, if you’re measuring the length of a pencil multiple times, you might get slightly different values each time due to small variations in how you hold the ruler or where you start the measurement. Random errors can be reduced by taking multiple measurements and calculating an average.
Gross Errors: These are significant errors that result in measurements that are way off from the true value. Gross errors can occur due to mistakes in reading instruments, recording data incorrectly, or even deliberate tampering. For example, if you accidentally record a temperature reading of 100 degrees Celsius instead of 10 degrees Celsius, that would be a gross error.
Understanding and identifying these types of errors is crucial in any scientific or mathematical endeavor because they can affect the validity and reliability of our results. By being aware of potential sources of error and taking steps to minimize them, we can ensure that our measurements are as accurate as possible.
Zero Error
Zero error-
If scale is worn out at zero mark then error will occur. Such error is called zero error.
Error can occur if scale is not placed along the length being measured.
Avoiding Zero Errors:
Calibration: Regularly calibrate your measuring instruments. Zero errors often occur when the measuring instrument doesn’t read zero when it should. Calibration ensures that the instrument is correctly zeroed before each measurement session.
Check Zero Reading: Always check that the instrument reads zero before taking any measurements. If it doesn’t, adjust it accordingly to ensure an accurate starting point.
Proper Handling: Handle the instrument carefully to prevent any accidental changes to the zero position. Avoid dropping or mishandling the instrument, as this can introduce zero errors.
Use Reference Objects: When possible, use reference objects with known dimensions to verify that the instrument is reading accurately. This can help detect and correct zero errors.
Parallax Error
Parallax error-
If the eye is not vertically above the point of measurement then parallax error will occur.
A personal error that arises due to the inclined view of the observer is called a parallax error.
To avoid parallax error it is better to keep shut one eye while making measurement.
Avoiding Parallax Errors:
Viewing Angle: Ensure that your eye is directly in line with the measurement markings on the instrument. Parallax errors occur when the observer’s eye is not perpendicular to the scale, causing an apparent shift in the position of the measurement.
Use Proper Lighting: Adequate lighting is essential to minimize parallax errors. Proper illumination helps ensure that there are no shadows or glare that could distort the measurement readings.
Close One Eye: Close one eye when taking measurements to eliminate any discrepancies caused by viewing the scale from an angle. This helps to ensure that your line of sight is perpendicular to the scale, reducing the chances of parallax errors.
Align Scales: If you’re using a device with multiple scales, such as a vernier caliper, make sure that the scales are aligned properly. Misalignment can lead to parallax errors when reading measurements from different scales.
Practice: Encourage students to practice taking measurements and observing the scale from different angles to develop the skill of minimizing parallax errors through proper positioning and viewing techniques.
Conclusion
Physical quantity-That which is to be measured is called physical quantity.
Fundamental quantities are those which can not be expressed in terms of other quantities.
Units of fundamental quantities are called fundamental units or basic units. There are seven fundamental units.
Derived quantity is that which can be obtained by the combination of fundamental quantities.
Units of derived quantities are called derived units.
Scalars are quantities that are fully described by a magnitude (or numerical value) alone.
They are quantities that have a magnitude or size, but they don’t have any direction associated with them.
Vector quantities are completely expresse3d by magnetude and direction both.They not only have a size or magnitude but also a direction.
An error may be defined as the difference between the measured and actual values.
Systematic Errors: These errors occur consistently and are often caused by flaws in the measuring device or the experimental setup.
Random errors-The errors that can be caused by fluctuations in environmental conditions, human error in reading instruments, or variations in the quantity being measured.
Gross Errors: These are significant errors that result in measurements that are way off from the true value.
Zero error-If scale is worn out at zero mark then error will occur. Such error is called zero error.
Parallax error-A personal error that arises due to the inclined view of the observer is called a parallax error.
This topic is useful for Homi Bhabha Jr. Scientist Exam, C.V Raman Science Talent Hunt Exam, Science Olympiad and other Science Competitive Exams.