GENERAL SCIENCE (PHYSICS)
ELECTRICITY
- Flow of electrons in a circuit is called Charge.
- Unit- Coulomb (C)
- 1 electron = 1.6 × 10⁻¹⁹ C
- 1 C = 1/1.6 × 10⁻¹⁹ = 6 × 10¹⁸ electrons
- Unit- Ampere (A)
- I = Q/t = charge flowing per unit time
- Ammeter is used to measure flow of electric current in a circuit.
- Ammeter is always connected in series in the circuit.
Heat is the form of energy which produces the sensation of warmth.
Its SI unit is joule and other unit is calorie.
1 cal = 4.2 Joule
- The weight of a body remains same whether it is heated or cooled.
• The transfer of heat is always from hotter to colder body, i.e. from high temperature to low temperature.
Temperature
• Temperature is measure of hotness or coldness of a body.
• The heat flows from one body to another due to the difference in their body temperature.
- Absolute Zero temperature - temperature at which molecular motion ceases.
- At temperature – 40°C = – 40°F, Celsius scale is equal to Fahrenheit.
- The temperature at which the three phases of water remains at equilibrium is called triple point of water (273.16 K)
- Curie Point is the temperature at which metal loses magnetic properties.
- Pyrometer :- measure very high temperature
- Cryometer :- measure very low temperature, i.e below 0℃
- Thermocouple :- a kind of thermometer to measure temperature in electric circuit.
Thermometers
- The instruments used to measure temperature of a body is called thermometer.
- Clinical thermometer - It is used to measure human body temperatures and ranges from 96° F to 110°F or 35°C to 43°C.
Calorimetry
• Amount of heat required to raise the temperature of 1 g of
water by 1°C is called 1 calorie.
• Calorimetry states that heat lost by hotter body equals the
heat gained by colder body.
Specific Heat
• The amount of heat required to raise the temperature of
unit mass (m) of a substance through 1°C, is called its specific heat (s).
• It is denoted by s and its unit is ‘cal/g°C or Joule/g°/C.
• The specific heat of water is 4200 J/kg1/°C or 1000
cal/g1/°C – which is high compared with most other substances. Therefore,
water is used as coolant in radiator in vehicle and hot water is used for the fermentation.
- Heat energy given or taken to change the temperature of a body is given by
Q = ms∆θ
where, m = mass of the body
∆θ = change in temperature.
The amount of heat required to raise the temperature of 1
mole of a gas by 1°C is called molar specific heat.
- Specific heat depends on nature of the body or materials.
👉 Cooking utensils are made of Aluminium, Brass, Steel, because these substances have low specific heat and high thermal conductivity.
Latent Heat
- The heat energy absorbed or released at constant temperature per unit mass for change of state, is called latent heat.
- It is denoted by L and its SI unit is cal/g or kcal/kg.
- Heat energy absorbed or released during change of state is given by
Q = mL
where, m = mass of the substance.
- Latent heat of fusion of ice is 80 cal/g.
- Latent heat of vaporisation of steam is 536 cal/g.
- A gap is provided in between two consecutive railway tracks.
- Concrete floors are laid in form of small sections.
- Telephone and telegraph wires get slackened in summer and become tight in winter.
- Metal tyre of wooden wheel of a cart is made smaller than the size of wheel.
- Chimney of a burning lamp cracks when a drop of water is put over it.
- Conduction :- in solids, process is slow
- Convection :- in liquids & gases , process is also slow.
- Radiation :- heat from sun, heat transmission at the speed of light.
- Double walled glass bottle used in a thermoflask.
- White cloths are preferred in summer.
- It is warmer on a cloudy night, because heat radiated by earth is obstructed and sent back to atmosphere.
- The door of an operating refrigerator in a room is opened, the temperature of room will be raised.
- Relative humidity increases with increases in temperature.
- If a thermoflask containing tea is shaken vigorously, temperature of tea rises, because of increase in internal energy.
Process of conversion of States
- Solid to Liquid - Melting
- Liquid to Solid - Freezing
- Liquid to Gas - Boiling
- Gas to Liquid - Condensation
- Solid to Gas - Sublimation
- Gas to Solid - Deposition
- During summer, water kept in an earthen pot becomes cool because of the phenomenon of Evaporation.
- The rate of evaporation decreases with increases in humidity.
- When alcohol is applied on the forehead of a person having high temperature, the temperature reduces, because alcohol while evaporating draws the heat out of the body.
- It states that the rate of cooling is directly proportional to the temperature difference of the body and its surroundings.
- It is used to determine the specific heat of liquid.
- This law is valid for small temperature difference.
LIGHT
Wave :- A wave is a disturbance which propagates energy from one place to other, without transportation of matter.
Types : -
- Mechanical waves- medium dependent
- Electromagnetic waves- medium independent
- Light is an example of EM Wave.
- Light travels through a straight path and maximum in air/vacuum (3 × 10⁸ m/s)
- Rarer medium- speed of light & wavelength are high.
- Denser medium- speed of light &wavelength are low.
- Real image - through which the rays of light actually pass & which can be formed on a screen. Ex- Cinema Screen
- Virtual image - through which the rays of light do not actually pass, although they appear to pass. Ex- images formed in Plane Mirror
REFLECTION OF LIGHT (Law of Reflection)
(i) The angle of incidence is equal to the angle of
reflection.
(ii) The incident ray, the normal, the point of incidence and the reflected ray, all lie in the same plane.
i.e. medium remains unchanged.
- The ratio between the angle of incidence and the angle of reflection is 1 : 1.
- If a light ray falls on a plane mirror normally, the angle of reflection will be 90°.
Mirror :- a highly polished surface from which most of light is reflected.
Types :-
- Plane mirror
- Spherical mirror - Concave mirror & Convex mirror
Plane mirror
- virtual image & laterally inverted
- size of object = size of image
- To see full image in a plane mirror, a person requires a mirror of at least half of its height.
- When a plane mirror is rotated through an angle ϕ, then the image is rotated through an angle of 2ϕ.
- Use :- sextant, kaleidoscope, optical instruments & looking glass
- No. of images formed in between two parallel mirrors is infinity (∞).
Spherical Mirrors
- Concave Mirror :- Images are real, inverted & magnified.
Uses of concave mirrors
• torches, search-lights and vehicles headlights to get powerful parallel beams of light.
• shaving mirrors and make-up glass to see a larger image of the face.
- The dentists use concave mirrors to see large images of the teeth of patients.
- used in Ophthalmoscope
• Large concave mirrors are used to concentrate sunlight to produce heat in solar furnaces.
2. Convex Mirror :- Images are virtual, erect & diminished.
Uses of convex mirrors
- rearview (wing) mirrors in vehicles, enabling the driver to see traffic behind him/her to facilitate safe driving.
- Also, they have a wider field of view as they are curved outwards.
- sodium reflector lamp.
REFRACTION OF LIGHT
The bending of ray of light passing from one medium to another medium, called refraction.
i.e:- medium changed (medium dependent)
The following are the laws of refraction of light:
(i) The incident ray, the refracted ray and the normal to the interface of two transparent media at the point of incidence, all lie in the same plane.
(ii) The ratio of sine of angle of incidence to the sine of angle of refraction is a constant, for the light of a given colour and for the given pair of media. This law is also known as Snell’s law of refraction.
If i is the angle of incidence and r is the angle of refraction, then,
Sin i/Sin r = constant = refractive index (r.i)
r.i = speed of light of vaccum / speed of light in the medium
- The r.i of light of the medium depends on optical density of that medium. (r.i of air = 1, r.i of water = 1.33, r.i of glass = 1.5, r.i of diamond = 2.42)
Application of refraction
- From earth's surface, the stars appear to twinkle
- a stick immersed in water appears bent
- a pond looks shallower (less deepen)
- a person looks shorter when he is standing in water
- A lemon kept in water in a glass tumbler appears to be bigger than its actual size, when viewed from the sides.
When a ray of light passes from one medium to other, then its frequency and phase don't change, but the wavelength & wave velocity change.
- Optically denser medium - larger refractive index & speed of light is low
- Optically rarer medium - lower refractive index & speed of light is high
- The speed of light is higher in a rarer medium than a denser medium.
The twinkling effect of straight light is due to change in temperature of the stars.
- The colour of stars is an indication of its temperature.
- Stars would be seen clearly if we cross the earth and sky.
- The brightness of a star depends on its size, temperature and distance from the earth.
TOTAL INTERNAL REFLECTION
Total internal reflection is a phenomenon that occurs when light travels from a more optically dense medium to a less optically dense one, such as glass to air or water to air.
Applications of Total Internal Reflection -
- Sparkling of diamond, when light incident on it.
- Mirage and looming forming
- Shining of air bubbles in water
- Optical fiber in telecommunications
- Functioning of Periscope
(Diamond sparkling- due to high refractive index.)
DISPERSION
When a ray of white light is passed through the prism, it gets splitted into its constituent colours. The splitting of light into its component colors is called dispersion.
- The sequence of colors VIBGYOR.
- Different colors of light bend through different angles with respect to the incident ray, as they pass through a prism.
The band of colours formed, which are decreasing order of wave length and increasing order of frequency, called Spectrum.
- The red light bends the least while the violet the most. Thus, the rays of each colour emerge along different paths and thus become distinct. It is the band of distinct colors that we see in a spectrum.
Application : - A rainbow is a natural
spectrum appearing in the sky after a rain shower. It is caused by dispersion
of sunlight by tiny water droplets, present in the atmosphere. A rainbow is always
formed in a direction opposite to that of the Sun.
The water droplets act like
small prisms. They refract and disperse the incident sunlight, then reflect it
internally, and finally refract it again when it comes out of the raindrop.
Due to the dispersion of
light and internal reflection, different colors reach the observer’s eye.
SCATTERING OF LIGHT
Scattering of light is the
phenomenon by which a beam of light is redirected in many different directions
when it interacts with a particle of matter.
Scattering maximum - Violet (when frequency is more, wavelength is less) &
Scattering minimum - Red (when frequency is less, wavelength is more)
Application :-
- The blue colour of the sky
- colour of water in deep sea
- the reddening of the sun at sunrise and the sunset
- Scattering of light in the atmosphere takes place due to presence of dust particles.
- Advanced sunrise and delayed sunset found in the sky are due to refraction of light.
Mirrage - Mirrage is an optical phenomenon caused by the total internal reflection of light from distant objects. When light passes from cold air (denser) to hot air (rarer), it bends away from the normal and undergoes total internal reflection, thus causes an illusion to the observer that, light is coming from the ground.
Looming - It is a kind of mirage observed in very cold regions in which a distant object appears to be hanging mid way in the air. It is produced by total internal reflection of light caused by atmospheric refraction.
Tyndall Effect :- The Tyndall effect is the scattering of light as a light beam passes through a colloid. The individual suspension particles scatter and reflect light, making the beam visible.
- The earth’s atmosphere is a heterogeneous mixture of minute particles like smoke, tiny water droplets, suspended particles of dust and molecules of air. When a beam of light strikes such fine particles, the path of the beam becomes visible.
- Tyndall effect is seen when a fine beam of sunlight enters a smoke-filled room through a small hole.
- Tyndall effect can also be observed when sunlight passes through a canopy of a dense forest.
Power of Accommodation of Eye - The ability of the lens to change its shape to focus near and distant objects is called accommodation. A normal human eye can see objects clearly that are between 25 cm and infinity.
- Persec an astronomical unit to measure distance.
Lens : - 2 types
- Concave Lens : - diverging in nature
- Convex Lens : - converging in nature
- Convex lens has +ve focal length & real focal point (+ve power).
- Concave lens has - ve focal length & -ve power.
- Myopia or short-sightedness :- Nearby objects can be seen more easily. Eyeglasses with concave lenses correct this problem by diverging the light rays before they enter the eye. Nearsightedness is called myopia.
- Hypermetropia or far-sightedness :- Eyeglasses with convex lenses can correct the problem. Farsightedness is called hypermetropia.
- Presbyopia :- In this defect both near and far objects are not clearly visible. This can be removed by using bifocal lens.
- Astigmatism :- Here eye can't see horizontal & vertical lines clearly. This can be removed by cylindrical lens.
SOUND
Mechanical waves are of two types.
1. Transverse Wave: If the particles of the medium vibrate perpendicular to the direction of propagation of wave, the wave is called transverse wave.
- Here creast and trough are occurred.
Example:- Waves on strings under tension, waves on the surface of water.
2. Longitudinal wave: If the particles of the medium vibrate in the direction of propagation of wave, the wave is called longitudinal wave.
- Here compression and rarefraction are occurred.
Example:- Sound waves in air, waves on spring, vibration in tuning fork.
Sound
Sound waves are mechanical longitudinal
waves and require medium for their propagation. It cannot propagate through
vacuum. When propagated, speed and wavelength changes, but frequency remains
constant.
It is of three types on the basis of frequency range:
- Infrasonic waves – < 20 Hz
- Audio waves – 20 to 20,000 Hz
- Ultrasonic waves – >20,000 Hz
Uses of Ultrasonic waves
- Sending signals
- Ultrasonography
- Measuring depth of sea
- Sterilisation of liquid
- Aeroplanes
- Bats fly in the dark
- Utilision for monitoring earthquakes
- Used in Seismograph
Properties of Sound Wave
1. Reflection
- The bouncing back of sound when it strikes a hard surface, is called reflection of sound.
- The laws of reflection of light are also obeyed during reflection of sound.
- The working of megaphone, sound boards and ear trumpet is based on reflection of sound.
- The repetition of sound due to reflection of sound waves, is called an echo.
- The persistence of hearing on human ear is 1/10th of a second.
- The minimum distance from a sound reflecting surface to hear an echo is nearly is nearly 17 m.
- Sound proof rooms are made of two layers of walls having vacuum between them.
- Reverberation arises due to multiple reflection of sound.
- While designing an auditorium for speech or musical concerts, one has to take proper care for the absorption and reflection of sound.
- Time taken by reverberant sound to decrease its intensity by a factor of 106 is called reverberation time.
2. Refraction
- When a sound wave move from one mechanical medium to another mechanical medium, it shows deviation from the original path of the incident wave. The phenomenon is called refraction. It is due to difference is speed of sound in media.
3. Diffraction
- When sound waves originated by a vibrating source, they spread in the medium and if the medium is homogeneous, this leads to bending of sound waves around the edges. Which is known as diffraction.
- The sound waves diffracted broadly and one can easily hears the voice of the another person.
Musical Scale
In theory of music, a musical scale is a
set of musical notes by the frequencies of which are in simple ratios to one
another. Sa, re, ga, ma, pa, dha, ni is one such scale called the diatonic
scale. The interval sa-sa is called an octave (8).
Doppler’s Effect
The apparent change in the frequency of
source due to relative motion between the source and observer is called
Doppler’s effect.
Applications of Doppler’s Effect
The measurement of Doppler shift (based on Doppler’s
effect) has been used -
- By police to check over speeding of vehicles.
- At airports to guide the aircraft.
- To study heart and blood flow in different parts of the body.
- By astrophysicist to measure the velocities of planets and stars.
SONAR
- SONAR stands for Sound Navigation And Ranging. It is used to measure the depth of a sea, to locate the enemy submarines and shipwrecks.
- The transmitter of a sonar produces pulses of ultrasonic sound waves of frequency of about 50000 Hz. The reflected sound waves are received by the receiver.
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