Physics Physics Physics Physics PhysicsPhysics Physics

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1. Measurement Measurement is the basis of all important scientific study. It plays an important role in our daily life also. While finding your height, buying milk for your family, timing the race completed by your friend and so on, you need to make measurements. Measurement answers questions like, how long, how heavy and how fast? Measurement is defined as the determination of the size or magnitude of a quantity.

2. Physical quantity & Units Physical quantity is a quantity that can be measured. Physical quantities can be classified into two: fundamental quantities and derived quantities. Quantities which cannot be expressed in terms of any other physical quantities are called fundamental quantities. Example: Length, mass, time, temperature etc. Quantities which can be expressed in terms of fundamental quantities are called derived quantities. Example: Area, volume, density etc.

3. Units A unit is a standard quantity with which the unknown quantities are compared.

4. Derived quantities

5. Temperature Temperature is the measure of hotness or coldness of a body. SI unit of temperature is kelvin (K). Zero kelvin (0 K) is commonly known as absolute zero. The other units for measuring temperature are degree celsius (°C) and fahrenheit (F).

6. Measuring Instrucments LEAST COUNT : The smallest length which can be measured by metre scale is called least count. Usually the least count of a scale is 1 mm. We can measure the length of objects upto 1 mm accuracy with this scale. By using Vernier caliper we can have an accuracy of 0.1 mm and with screw gauge we can have an accuracy of 0.01 mm.

7. Vernier caliper The Vernier caliper consists of a thin long steel scale graduated in cm and mm called main scale. To the left end of the main scale an upper and a lower jaw are fixed perpendicular to the bar. These are named as fixed jaws. To the right of the fixed jaws, a slider with an upper and a lower moveable jaw is fixed. The slider can be moved or fixed to any position using a screw. The Vernier scale is marked on the slider and it moves along with the movable jaws and the slider. The lower jaws are used to measure the external dimensions and the upper jaws are used to measure the internal dimensions of the objects. The thin bar attached to the right side of the Vernier scale is used to measure the depth of hollow objects.

8. Usage of Vernier caliper

9. Zero error Unscrew the slider and move it to the left, such that both the jaws touch each other. Check whether the zero marking of the main scale coincides with that of the zero of the vernier scale. If they coincide then there is no zero error. If they do not coincide with each other, the instrument is said to possess zero error. Zero error may be positive or negative. If the zero of a vernier is shifted to the right of main scale, it is called positive error. On the other hand, if the zero of the vernier is shifted to the left of the zero of main scale, then the error is negative.

10. Positive zero error : From the figure you can see that zero of the vernier scale is shifted to the right of the zero of the main scale. In this case the reading will be more than the actual reading. Hence, this error should be corrected. In order to correct this error, find out which vernier division is coinciding with any of the main scale divisions. Here, fifth vernier division is coinciding with a main scale division. So, positive zero error = +5 × LC = +5 × 0.01 = 0.05 cm and the zero correction is negative. Hence, zero correction is –0.05 cm.

11. Negative zero error: You can see that the zero of the vernier scale is shifted to the left of the zero of the main scale. So, the obtained reading will be less than the actual reading. To correct this error we should first find which vernier division is coinciding with any of the main scale divisions, as we found in the previous case. In this case, you can see that sixth line is coinciding. To find the negative error, we can count backward (from 10). Here, the fourth line is coinciding. Therefore, negative zero error = –4 × LC = –4 × 0.01 = –0.04 cm. Then zero correction is positive. Hence, zero correction is +0.04 cm.

12. Digital Vernier caliper We are living in a digital world and the digital version of the Vernier callipers are available nowadays. Digital Vernier caliper has a digital display on the slider, which calculates and displays the measured value. The user need not manually calculate the least count, zero error etc.

13. Screw gauge Screw gauge is an instrument that can measure the dimensions upto 1/100th of a millimetre or 0.01 mm. With the screw gauge it is possible to measure the diameter of a thin wire and thickness of thin metallic plates.

14. Screw gauge The screw gauge consists of a U shaped metal frame. A hollow cylinder is attached to one end of the frame. Grooves are cut on the inner surface of the cylinder through which a screw passes. On the cylinder parallel to the axis of the screw there is a scale which is graduated in millimetre . It is called Pitch Scale (PS). One end of the screw is attached to a sleeve. The head of the sleeve (Thimble) is divided into 100 divisions and it is called the Head scale.

15. The end of the screw has a plane surface (Spindle). A stud (Anvil) is attached to the other end of the frame, just opposite to the tip of the screw. The screw head is provided with a ratchat arrangement (safety device) to prevent the user from exerting undue pressure.

16. Screw gauge The screw gauge works on the principal that when a screw rotates in a nut, the distance moved by the tip of the screw is directly proportional to the number of rotations.

17. FLUIDS In SI units, the unit of thrust is newton (denoted as N). The unit of pressure is newton per square metre or newton metre –2 (denoted as Nm–2).

18. Factors determining liquid pressure in liquids Pressure exerted by a liquid at a point is determined by, depth of the liquid (h) (ii) density of the liquid (ρ) (iii) acceleration due to gravity (g).

19. From this we can infer that pressure varies as depth increases. But, it is same at a particular depth independent of the direction.

20. Pascal's Law Pascal's principle is named after Blaise Pascal (1623-1662), a French mathematician and physicist. The law states that the external pressure applied on an incompressible liquid is transmitted uniformly throughout the liquid. Pascal’s law can be demonstrated with the help of a glass vessel having holes all over its surface. Fill it with water. Push the piston. The water rushes out of the holes in the vessel with the same pressure. The force applied on the piston exerts pressure on water. This pressure is transmitted equally throughout the liquid in all directions .This principle is applied in various machines used in our daily life.

21. Density The density of a substance is the mass per unit volume of a given substance. The SI unit of density is kilogram per meter cubic (kg/m3 ) also gram per centimeter cubic (g/cm3 ). The symbol for density is rho (ρ). Floating and sinking Whether an object will sink or float in a liquid is determined by the density of the object compared to the density of the liquid. If the density of a substance is less than the density of the liquid it will float. For example a piece of wood which is less dense than water will float on it. Any substance having more density than water (for example, a stone), will sink into it.

22. Hydrometer A direct-reading instrument used for measuring the density or relative density of the liquid is called hydrometer. Hydrometer is based on the principle of flotation, i.e., the weight of the liquid displaced by the immersed portion of the hydrometer is equal to the weight of the hydrometer

23. Archimedes' Principle Archimedes principle is the consequence of Pascal’s law. According to legend, Archimedes devised the principle of the 'hydrostatic balance' after he noticed his own apparent loss in weight while sitting in his bath. The story goes that he was so enthused with his discovery that he jumped out of his bath and ran through the town, shouting 'eureka’. Archimedes principle states that ‘a body immersed in a fluid experiences a vertical upward buoyant force equal to the weight of the fluid it displaces’.

24. Barometer is an instrument used to measure atmospheric pressure. Pascal’s law states that an increase in pressure at any point inside a liquid at rest is transmitted equally and without any change, in all directions to every other point in the liquid. ™ Archimedes’ principle states that when a body is partially or wholly immersed in a fluid, it experiences an up thrust or apparent lose of weight, which is equal to the weight of the fluid displaced by the immersed part of the body. ™ Density is known as mass per unit volume of a body. Its S.I. unit is kg m–3.

25. HEAT All substances in our surrounding are made up of molecules. The sum of the kinetic and potential energy is called the internal energy of the molecules. This internal energy, when flows out, is called heat energy. This energy is more in hot substances and less in cold substances and flows from hot substances to cold substances.

26.   Effects of Heat When a substance is heated, the following things can happen. When heat is added to a substance, the molecules gain energy and vibrate, and force other molecules apart. As a result, expansion takes place. You would have seen some space being left in railway tracks. It is because, during summer time, more heat causes expansion in tracks. Expansion is greater in liquids than solids and it is maximum in gases.

27. Temperature Temperature is the degree of hotness or coolness of a body. Hotter the body, higher is its temperature. Unit of Temperature The SI unit of temperature is kelvin (K). For day to day applications, Celsius (°C) is used. Temperature is measured with a thermometer. Temperature scales There are three scales of temperature. i . Fahrenheit scale ii. Celsius or Centigrade scale iii. Kelvin or Absolute scale

28. Kelvin scale Kelvin scale (Absolute scale) Kelvin scale is known as the absolute scale. On the Kelvin scale 0 K represents absolute zero, the temperature at which the molecules of a substance have their lowest possible energy. The formula for converting a Celsius scale to Kelvin scale is: K = C+273.15

29. Specific Heat Capacity specific heat capacity of a substance is defined as the amount of heat required to raise the temperature of 1 kg of the substance by 10 C or 1 K. The SI unit of specific heat capacity is Jkg-1 K-1. The most commonly used units of specific heat capacity are J/ kg°C and J/ g°C .

30. GASES The three fundamental laws which connect the relation between pressure, volume and temperature are as follows: 1) Boyle’s Law 2) Charles's law 3) Avogadro's law

31. Boyle’s law: When the temperature of a gas is kept constant, the volume of a fixed mass of gas is inversely proportional to its pressure. P α 1/V PV = constant

32. Charles's law Charles’s law was formulated by a French scientist Jacques Charles. According to this law, When the pressure of gas is kept constant, the volume of a gas is directly proportional to the temperature of the gas. V α T V/T = constant

33. Avogadro's law Avogadro's law states that at constant pressure and temperature, the volume of a gas is directly proportional to number of atoms or molecules present in it. V α n (or) V/n = constant Avogadro’s number (NA) is the total number of atoms per mole of the substance. It is equal to 6.023 × 10^23 /mol.

34. Ideal gases If the atoms or molecules of a gas do not interact with each other, then the gas is said to be an ideal gas or a perfect gas. Ideal gases obey Boyle’s law, Charles’s law and Avogadro’s law.

35. Laws of a Simple Pendulum A simple pendulum has a small-diameter bob and a string that has a very small mass but is strong adequate not to stretch significantly. The period of a simple pendulum is given by T = 2π √l/g Where, l = Length of a simple pendulum; g = acceleration due to gravity. From the equation, we can write the relation between the time period of a pendulum and acceleration due to gravity as T is inversely proportional to √g. This relation is referred to as the fourth law of the simple pendulum. In ideal theory, the suspending material will have no mass but in realism that is not feasible.

36. Pendulum

37. 1 st  law or the law of isochronism: The time period of the simple pendulum is independent of the amplitude, provided the amplitude is sufficiently small. This property is known as the law of isochronism. The time period (T) is constant when effective length (L) and gravity (g) are constants. This means that a pendulum will take same time in completing each oscillation, whatever is the amplitude, provided the latter does not exceed 4 o . So the time period of oscillation of a  simple pendulum  is independent of the amplitude of vibration, provided its amplitude does not exceed 4 o . The oscillation of the simple pendulum is isochronous.

38. 2 nd  law or the law of length: The time period of the simple pendulum is directly proportional to the square root of its length. This property is known as the law of length. When acceleration due to gravity (g) is constant, the time period (T) of oscillation of a simple pendulum is directly proportional to the square root of its effective length (L). The period of oscillation of a simple pendulum of constant length is independent of its amplitude, provided the amplitude is small. So, T ∞ √L, when g is constant.

39. 3 rd  law or the law of acceleration: The time period of a simple pendulum is inversely proportional to the square root of the acceleration due to gravity at that place. This property is known as the law of acceleration due to gravity. When effective length (L) is constant, the time period (T) of oscillation of a simple pendulum is inversely proportional to the square root of the acceleration due to gravity (g) at a place of observation. So, T ∞ √1/g, when L is constant.

40. 4 th  law or the law of mass: The time period of oscillation of a pendulum at a place independent of mass and material of the bob provided the effective length of the pendulum is constant. As the expression doesn’t contain the term ‘m’, the time period of the simple pendulum is independent of the mass and material of the bob. This property is known as the law of mass. Uses of Simple Pendulum Since the time period of a simple pendulum depends on the length and acceleration due to gravity at a given place, it is used to determine the time in clocks that work on the standard of the simple pendulum. It is also used to find out the acceleration due to gravity at a place.