# Science ## Wave and Optics Short Questions Answers

#### 1. Why is a diver underwater unable to hear the sound produced in the air outside?

When sound travels from air to water, a large portion of sound energy produced in the air reflects from the water surface and only a little fraction of incident intensity (= 0.1 %) enters water suffering refraction. So, the diver underwater cannot get a distinct impression of any sound.

#### 2. What are mechanical waves and electromagnetic waves? Give some examples.

The waves which require some material medium to travel are called mechanical waves. Eg: Sound Waves, Waves in a string or a rope under tension, etc.

Electromagnetic Waves are those waves that can propagate even in empty space, where there is no medium. Eg: Light waves, Radio waves, Infrared and ultraviolet radiation, etc.

#### 3. What are transverse and longitudinal waves?

If the particles of the medium vibrate perpendicular to the direction of propagation of the wave, the waves are called Transverse Waves. A transverse wave travels forming crests and troughs. If the particles of the medium vibrate along (to and fro) the direction of propagation of the Waves, the waves are called Longitudinal Waves. A longitudinal Wave travels forming compressions and rarefactions.

#### 4.  Longitudinal waves are also called pressure waves. Why?

If the particles of the medium vibrate along (to and fro) the direction of propagation of the waves, the waves are called Longitudinal Waves. When they vibrate to and fro, they cause compression in the region in front of the vibrating particles and refraction to the backside. So wherever they go, they create regions of high pressure and low pressure. So, they are called Pressure Waves.

#### 5. Distinguish between progressive and stationary waves.

Progressive Waves are those waves that carry energy along with them from one place to another. The transfer of energy occurs along with crest – troughs or compression – rarefactions.

Stationary Waves are those which can not carry energy from one end to other. Energy in stationary waves is confined between nodes.

#### 6. Do sound waves undergo reflection, refraction, and polarization phenomena? [HSEB 2062]

Sound wave undergoes reflection and refraction but it does not follow polarization. Since a sound wave is a longitudinal wave, the vibration of particles occurs to and fro in the direction of the propagation of the wave. The vibrations of such type cannot be limited or controlled by any barriers and so polarization is not possible in them.

#### 7. Do sound waves need a medium to travel from one point to other in space? What properties of the medium are relevant? [HSEB 2062]

The plain answer is ‘YES’. Sound waves are mechanical waves and they travel by means of push and pull existing between particles, without which the compressions and rarefactions cannot transmit. The relevant properties are the elastic and inertial properties, as is shown by various relations for velocities of sound as v = √k/p = √γP/ρ (in air or gas)• v = √γ/ρ (in solid bars), v= √T/m (in stretched strings), etc.
The elastic properties determine how fast or slow the molecules return ed to the same position after being displaced by the neighboring particle. The inertial property determines how difficult it is to move the particle or stop it after it has started moving.

#### 8. Although the density of a solid is high, the velocity of sound is greater in a solid, explain.

The velocity of sound in a solid is given by
v = √E/ρ

Where E and ρ are the elasticity and density of the solid respectively. For a solid, E takes a higher value than ρ i.e. the ratio of E/ρ will be more. so, in selling, the velocity of sound is the greater velocity of sound is greater although its density is high.

#### 9. Explain why the flash of light reaches the earth before the sound comes from the same thunder.

This phenomenon depends on the comparative speed of light and sound through air. The velocity of tight from lightning through the air is almost 3×108 m/s, so the flash reaches earlier. However, the velocity of the sound of lightning travels with a speed of around 340m/s according to the V(in the air) = √γP/ρ . So, this sound reaches later than the flash.

#### 10. What discrepancy was there in Newton’s formula for the velocity of sound in the air?

Isaac Newton assumed that when sound traveled through the air, the vibration of air molecules cause isothermal expansion and compression because he observed that the temperature of air remained constant. He then obtained a formula for the determination of the velocity of sound, expressed as V(in the air) = √P/ρ .

When standard values were used for P (air) and ρ (air) (1.01 × 10^5N/m^2) and 1.293 kg/m^3 respectively), the velocity of sound came to be 279.49m/s. This value did not agree with the experimentally observed value of about 330m/s. So, it was argued that the very theoretical basis of Newton’s formula should have been wrong.

#### 11. A person walking on a railway line hears two sounds of the same explosion occurring far away, why?

The phenomenon is due to two paths used by sound to reach the listener – one is the metal some form of iron) of the railway line and the other is the air. When the sound of an explosion travels through metal, the velocity will be high (about 5000m/s), making the time required to travel very less. For sound traveling through the air, the velocity of sound will be less (about 330m/s) and so • takes more time to travel. So, the listener will hear the sound twice.

#### 12. When a person hammers at one end of a metal pipe and a listener places his ear at the other end, two di ct sounds are heard. Why?

The phenomenon is also due to two paths used by sound to reach the listener – one is the metal pipe itself and the other is the air. When the sound of an explosion travels through metal, the velocity will be high (about 2000 to 5000m/ s), making the time required to travel very, less. For sound traveling through the air, the velocity of sound will be less (about 330m/ s} and so it takes more time to travel. So, the listener will hear the sound twice.

13. Velocity of sound increases on a cloudy day. Why?  [HSEB 2066]
Such phenomenon is due to the addition of moisture on-air and an increase in velocity of sound in such air. Clouds contain a lot of water vapor in them. If a day is cloudy, the added water vapor in the air reduces the density. Then according to the relation V(in the air) = √γP/ρ, the velocity of sound will be more. ## Velocity Time Graph: Velocity Vs Time Graph

#### (a) Distance – Time (x — t) Graph: Velocity

A plot of distance against time is called a distance-time graph. The velocity of a particle at any point can be found from the graph of its position as a function of time. For a uniform motion, the distance-time graph is a straight line as shown in fig 1 (i) whereas for non-uniform motion it is as shown in fig 1 (ii).

The distance-time graphs is used to determine

• Position of a body at any time.
• Distance covered by a body in any interval of time.
• Speed of the body at any instant of time.
• The slope of the x – t graph at any point gives the instantaneous velocity of the body.

#### Velocity – Time (v – t) Graph: Acceleration

A plot showing the variation of velocity as a function of time is called the velocity-time (v – t) graph. The velocity-time graph for a body moving with constant speed in a straight line is a straight line parallel to the time axis as shown in fig.3(i)

The velocity-time graph for a body moving with a constant acceleration having initial velocity zero is a straight line passing through the origin as shown in fig. 2 (i). However for a body having non-zero initial velocity, the v – t graph look like in fig 2 (i).

The velocity-time graph for a body moving with non-uniform acceleration is as shown in fig 3 (ii)

The v-t graph can be used to determine the acceleration of the body at any instant of time. Referring to fig.3(ii), if we have to find the acceleration at point P, we draw a tangent AB at point P. The slope of tangent BC/AC gives the acceleration. Similarly, this graph can be used to find the velocity of the body at any instant of time.

We know, from the definition, of instantaneous velocity,v = dx/dt.

This equation can be inverted to find the displacement in the same interval of time.

The geometrical meaning of the above equation is that it gives the area under the v-t curve in the interval Δt = t2 – t1 (referring to fig.4). The shaded region represents the displacement of the body in the time interval Δt = t2 – t. ## Enzyme Inhibition: Enzyme Inhibition Types Graphs and Examples

A wide variety of compounds can reduce enzyme activities. These compounds are called enzyme inhibitors. Enzyme inhibitors bind to the enzyme and reduce their activity. The process is called Enzyme Inhibition.

## Enzyme Inhibition Types

There are 3 types of enzyme inhibitions

1. Competitive enzyme inhibition

2. Non Competitive enzyme Inhibition

3. Un Competitive enzyme Inhibition

### 1. Competitive enzyme inhibition

In competitive enzyme inhibition, the inhibitors is structurally similar to the substrate (substrate analogue). Hence inhibitor competes with the substrate for binding with the active site of enzyme.

The binding of inhibitors to active site of the enzymes prevents the substrate from the binding with enzyme, which results in decrease ES formation and reduced rate of enzyme reaction.

The formation of ES complex or EI complex depends upon the relative concentration of substrate and inhibitors. Competitive enzymes inhibition is reversible. It can be overcome by high substrate concentration. Thus competitive enzyme inhibition does not alter the Vmax, but increase the Km value.

#### Example:

Malonate is the competitive inhibitor of succinate dehydrogenase enzyme. Succinate dehydrogenase enzyme converts succinate to fumurate. Malonate has a structure similar to succinate, hence competes with succinate to bind with succinate dehydrogenase. Hence malanote competitively inhibits succinate dehydrogenase enzyme.

Note: The structure of malonate is similar to succinate. So, Malonate competes with succinate to bind with competitive site of succinate dehydrogenase enzyme, hence competitively inhibits the enzyme.

#### Biomedical importance of competitive enzyme inhibition:

The mechanism of competitive enzyme inhibition is used in chemotherapy (treatment with the help of chemical compounds) of certain diseases. These are synthetic chemical compounds, which are designed to have structures similar to desired substrates whose reaction needs to be competitively inhibited. These compounds, when ingested, competitively inhibit specific enzymes blocking the unwanted reactions. (Such compounds are referred to as ‘Antimetabolites’).

Examples are,

1) Treatment of gout: Gout is a clinical condition caused due to the increased levels of uric acid in the blood and subsequent accumulation of uric acid in the joints causing severe pain (arthritis). The enzyme xanthine oxidase produces uric acid from hypoxanthine (which in turn is obtained from catabolism of purine nucleotides).

### 2. Non competitive enzyme inhibition:

In non-competitive enzyme inhibition, the inhibitor is not structurally similar to the substrate, hence does not compete with the substrates for the active site.

Types: Non-competitive enzyme inhibitions can be reversible or irreversible (generally irreversible). But both show similar kinetics.

a) Reversible non competitive enzyme inhibition

In Non-competitive enzyme inhibition, the inhibitor is not structurally similar to the substrate, hence does not compete with the substrates for the active site of the enzyme. The inhibitor may or may not bind with the active site. Instead it may (mostly) bind to the enzyme at a site other than the active site. Since S and I may combine at different sites, formations of both EI and ESI complexes are possible. Since ESI may breakdown to form products at a slower rate than does ES, the reaction may be slowed but not stopped. So Inhibitor does not interfere with the binding of substrate with the enzyme, but it lowers the maximum velocity attainable. So Km value is unchanged, but Vmax is lowered.

#### Examples:

1) Anti trypsin, non-competitively inhibits trypsin in reversible manner

2) Trypsin inhibitor present in soybean and ascaris worm

b) Irreversible non competitive enzyme inhibition (Enzyme poisons):

A varlet, of enzyme ‘poisons’, reduces the enzyme activity non-competitively. Here the inhibitor is not structurally similar to the substrate, but these inhibitors generally bind to the active site of enzymes (binds covalently) and inactivate them, which is irreversible. This process is not readily reversible by increasing the substrate concentration; however, the presence of substrates exerts a protective role by blocking or slowing the access of inhibitor to the active site. Usually, these enzyme poisons are not biological compounds.

#### Examples:

1) Inhibition of enzymes by heavy metals like Hg+2, Ag+, Pb+2, etc.

2) Inhibition of Enolase (A glycolytic enzyme) by fluoride

3) Inhibition of cytochrome oxidase enzyme by cyanide.

### 3. Uncompetitive Enzyme Inhibition

In uncompetitive enzyme inhibition, the inhibitors do not bind to free enzymes but can bind only to the ES complex and decrease the velocity of enzymatic reactions. Uncompetitive enzyme inhibitors decrease both Vmax and Km of enzymes.

#### Examples:

1. Inhibition of Placental alkaline phosphate enzyme by Phenylalanine

2. Inhibition of S-adenosyl methyl transferase by ATP ( In Yeast )

## Enzyme Inhibition Graphs ## Losses in Transformer

#### 1. What is an iron loss in a transformer and how it can be reduced?

In a transformer, a soft iron core is used. When a.c. current is pas through the transformer, eddy current is produced in the core and due to this will be the energy loss in the form of heat. This loss of one due to the iron core is known as iron loss. It can be reduced by laminating it.

#### 2. What is a copper loss in a transformer?

The wires of the primary and secondary coils are made of copper and have ohmic resistance. When current flows through the wires, the heat is generated. So some amount of electrical energy is lost in them for heat. This loss of energy due to the copper wire is known as copper loss.

#### 3. What is hysteresis loss in a transformer?

Due to alternating current, the magnetization and demagnetization of the iron core take place repeatedly over a complete cycle. During each le of magnetization and demagnetization, some energy is lost due to hysteresis and this amount of energy is equal to the area of the system pis loop. The energy loss due to hysteresis is called Hysteresis Loss.

#### 4. What is humming loss in a transformer?

When alternating current is passed through a transformer, the co of the transformer starts vibrating due to a change in a magnetic field produces a humming sound. Due to the production of sound, some p.d. of the electrical energy is lost. This loss of energy is known as humming loss in the transformer.

#### 5. What is flux loss in a transformer?

It is impossible to make a perfect coupling of the primary and secondary coils due to which whole of the magnetic flux produced by the primary coil never gets linked up with the secondary coil. It makes the loss of energy and this loss is known as flux loss.

#### 6. Can the use of a transformer be more economical in the transmission of a.c. to long-distance? Why?

In the transmission of a.c. to long distances, if line wire is used, the resistance of the wire will be considerable. There will be a loss of energy in the form of heat which is equal to I2R. i.e. it is proportional to the square of the current. But when we step up the a.c., it increases the voltage decreasing the value of current which decreases the loss of energy. Hence the use of the transformer can be more economical in the transmission of a.c. to long distances.

#### 8. What are the factors that reduce the efficiency of a transformer?

The efficiency of a transformer is reduced due to the following factors:

(a) Copper wires of the production of eddy current in the iron core, there will be loss of energy in the form of heat.

(b) Due to the production of eddy current in the iron core, there will be a loss of energy in the form of heat.

(c) Due to the magnetization and demagnetization of an iron core, there will be hysteresis loss which also appears in the form of heat.

(d) Due to the passage of a.c. current, the core of the transformer produces a humming sound which is also a cause of loss of energy.

#### 9. What are different power losses in a transformer? What measures do you take to minimize these losses? [HSEB 2062]

A transformer has various power losses. They are

(a) Copper loss

(b) Iron core loss

(c) Flux loss

(d) Humming loss

(e) Hysteresis loss

These power losses can be minimized by the following methods.

(a) Copper loss can be reduced by decreasing its resistance i.e. by using thick wires.

(b) Iron core loss can be reduced by laminating it.

(c) Flux loss can be reduced by coupling the primary and secondary coils perfectly as possible.

(d) Hysteresis loss can be reduced by choosing a proper material like silicon steel.

#### 11. A transformer gets heated up while in use. Why?

A transformer has various power losses. They are

(a) Copper loss

(b) Iron core loss

(c) Flux loss

(d) Humming loss

(e) Hysteresis loss

The most of the energy that is lost by a transformer is converted into heat which makes the transformer hot.

#### 12. What do you mean by a dc motor?

An electrical device that converts electrical energy into mechanical energy is called a motor. Here dc current is used to generate the mechanical energy. So it is called a dc motor.

#### 13. What is the search coil?

The search coil is a small coil of some 50 turns of fine insulated copper wire and about 1 sq. km. in the area wound over a small ebonite wooden frame. The area of cross-section of the coil is so small because the fields to be measured are usually non-uniform and also sometimes it has to be introduced into narrow gaps for the measurement of fields.

#### 14. What do you mean by electromagnetic damping?

In electricity measuring devices such as a moving coil galvanometer, the coil is wound on a metal frame. As the coil moves in the magnetic field, the eddy currents are induced in the frame. These eddy currents oppose the motion of the coil (Lenz’s law) and hence opposes the motion of the pointer attached to it. As a result, the pointer quickly attains the final position without oscillation. This kind of damping of the pointer due to the eddy currents is called eddy current damping or electromagnetic damping. ## Mutual Inductance

In this post, we have discussed short questions and answers of Mutual Inductance and transformer.

#### 1. A coil is wound on an iron core and looped back on itself so that the core has two sets of closely wound wires in series carrying current in the opposite direction. Why ?

A coil is wound on an iron core and looped back on itself so that the iron core has two sets of closely wound wires in series carrying current in the opposite direction because the self-inductance will be small due to cancellation of inductive effects. It is because the two sets of loops have the same current but in opposite directions and they have the self-induction in opposite direction.

#### 2. what is meant by mutual induction?

When two coils are placed close to each other and a varying current is passed through one of them, then the magnetic flux passing through the second coil will be changed due to a change in flux in the first coil which induces emf in the second coil. The phenomenon according to which an opposing emf is produced in a coil as a result of a change of current or magnetic flux linked with its neighboring coil is called Mutual Induction.

#### 3. On what factor does the mutual inductance between a pair of the coil depends?

The mutual inductance between a pair of the coil depends upon the following factors:

(a) The number of the primary coils and the number of secondary coils.

(b) The relative orientation of the coils.

(c) The permeability of the material of the core.

(d) The rate of change of current in the primary coil.

(e) The cross-sectional area of the coil.

#### 4. Define the coefficient of mutual induction for a pair of coils.

The property of two coils by virtue of which each opposes any change of current flowing in the other is called Mutual Inductance between the coils. We know ϕ   I where ϕ and I be the magnetic flux through the secondary coil and the current through the primary coil respectively.

or ϕ = MI

where M is a proportionality constant and is known as the coefficient of mutual inductance. M=ϕ/I Hence the coefficient of mutual inductance of two coils is numerically equal to the magnetic flux linked with the coil when unit current flows through the primary coil. Mutual inductance is measured in Henry in the SI system.

#### 5. How mutual induction is produced? Explain.

If a current is passed through primary coil P, a magnetic flux is set and a part of it links with secondary coil S. If the current in P is changed magnetic flux also changes, and hence an emf is produced in the secondary coil which is indicated by a galvanometer. The emf thus induced secondary coil is termed mutually induced emf and the process is called mutual induction. This induced emf also opposes the change in current in the primary coil.

#### 6. What are the advantages of a.c. over d.c.

A.c. has the following advantages over d.c. (a) A.c. can be transmitted at distant places without much loss in a.c. power but d.c. cannot be transmitted in this way. (b) Alternating voltages can be easily increased or decreased by using a transformer. (c) The generation of a.c. is economical than the generation of d.c. (d) A.c. can be easily converted into d.c. by the use of a rectifier.

#### 7. What is Fleming’s right-hand rule?

Fleming’s right-hand rule is used to determine the direction of induced emf (current) in a conductor. It states that if the thumb, the middle finger, and the forefinger of the right hand are stretched mutually perpendicular to each other in such a way that the thumb points in the direction of motion of the conductor and the fore-finger points in the direction of the magnetic field, the middle finger points in the direction of the induced emf in the conductor.

#### 8. A lamp connects with a coil of a larger number of turns and a battery in series does not light up to full brilliancy instantly on switching on the circuit. Why.

When the circuit is switched on, the current start growing through the coil at a rate (dl/dt), and a growing magnetic field is set up in it. It in turn produces an induced emf in the coil in the direction such that it opposes the growth of current in the circuit. As a result, the lamp glows less bright for an instant. When the current grows up to its maximum value, the current becomes constant and hence dl/dt becomes zero. The lamp then glows with full brilliancy as there is no induced emf in the coil.

#### 9. Two identical rings, one of the metallic and another non-metallic, are dropped from the same height. Which will reach the ground earlier?

There is a horizontal component of the earth’s magnetic field everywhere around the rings. When the metallic ring falls, it crosses the earth’s magnetic field. As a result, an induced emf is produced on it which opposes its downward motion. But, when a non-metallic ring falls, there is no induction in it, therefore falls faster than the metallic ring.

## Mutual Inductance Units

#### 10. What is the flux meter?

A flux meter is an instrument that can be used for measuring magnetic flux and hence magnetic field strength directly. It is a modified moving coil galvanometer having negligibly small mechanical damping and restoring couple but large electromagnetic damping.

#### 11. What is a transformer? On what principle does it work?

An electrical device that is used to convert low alternating voltage at high current into high alternating works g voltage at low current or vice-versa. It on the principle of mutual induction which states that if two coils are inductively coupled and when the current or magnetic flux is changed through one coil, then emf is induced in the second coil.

#### 12. Define step up and step down transformer. OR Distinguish between step-up and step-down transformer.

Step-up transformer – A transformer that covers low alternating voltage at high current into a high alternating voltage at low current. It has more number of turns in the secondary coil than in the primary turn. The primary coil is made of thick insulated copper wire whereas the secondary coil is made of then insulated copper wire. Step-up transformer is symbolized as Step down transformer – A transformer which converts in the primary coil. The high alternating voltage at low current into a low alternating voltage at high current. It has fewer turns in secondary coil than secondary coil is made of thick wire made of copper and the primary coil is made of thin copper wire.

#### 13. What is the ideal transformer?

A transformer which does not make any kind of energy loss is known as an ideal transformer. Here the input power is always equal to the output power and its efficiency is always 100%.

#### 14. We can not change the value of dc by the use of a transformer. Why?

When a d.c. the source is connected to the transformer, it provides a steady current to the primary coil and the magnetic field produced by it will also be steady. So there will be no mutual induction taking place between the primary and secondary coils which are necessary to change the value of current or voltage in output than in input. Also, the back emf will not be produced. So current will be maximum in the primary coil only which produces a large amount of heat in it. It can destroy the coil. Hence we can not change the value of dc by the use of a transformer.

#### 15. Write down the principle of a transformer.

A transformer works on the principle of mutual induction. It states that if two coils are inductively coupled and when current or magnetic flux is changed through one of the two coils, then emf is induced in the other coil.

#### 16. Why should the core of a transformer made of magnetic material of high permeability?

When the core of the transformer made of material of high permeability, the magnetic lines of force will crowd through the core, and the leakage of magnetic flux between the coils will be less which makes the magnetic flux through the secondary coil maximum and the energy loss due to the flux leakage will be minimum.

#### 17. In a step-up transformer, the primary coil is made from a thick wire. Why?

In a step-up transformer, the primary coil has less voltage than in the secondary coil and the current in the primary coil should be more than that in the secondary coil. So the resistance of the primary coil should be less than 1 and to get the resistance low, it should be thick since R A.

#### 18. Why is soft iron core whose hysteresis loop is narrow is used in making the core of a transformer?

When alternating current is passed through a transformer, the magnetization and demagnetization of the soft iron core take place. During this process, some amount of energy will be lost in a complete cycle which is equal to the area of the hysteresis loop. So if the soft iron core of a narrow hysteresis loop is used, the energy loss will be less. Hence to minimize the loss of energy, it is used in a transformer.

#### 19. What are eddy currents? Write down its uses. [HSEB 2063]

When a metal e.g. soft iron block is placed in a varying magnetic field, it induces a current in the metal whose direction is given by Lenz’s law. This induced current is called the Eddy Current or Foucault’s Current. Since this current opposes the cause which produces it, energy is lost in the form of heat and it can be reduced by laminating that metal. But it is useful for many purposes. They are used in

(a) Electromagnetic damping

(b) Induction motors

(c) Eddy current damping.

(d) Energy meters

(e) Induction heating

#### 20. Why is the core of a transformer laminated?

In electrical machines, metallic cores are used to increase magnetic flux but the changing magnetic flux produces large eddy currents and the cores are heated due to the flow of large eddy currents. The heat so produced is likely to damage the internal insulation besides causing loss of energy. To reduce the eddy currents, the cores are split into thin insulated sheets into planes parallel to the magnetic field. As the insulating layers offer very high resistances and the area of the conductor is reduced, the eddy currents set up are greatly reduced.