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201.

How will the magnetic field intensity at the centre of a circular coil carrying current change, if the current through the coil is doubled and the radius of the coil is halved ?

Answer»

SOLUTION :MAGNETIC FIELD at centre of a coil, B `prop (I)/(R)`, whencurrent I is doubled and radius R is halved, the magnetic field becomes four times the original field.
Discussion
202.

A doctor has prescribed a corrective lens of power + 1.5 D. Find the focal length of the lens. Is the prescribed lens diverging or converging ?

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SOLUTION :Given that POWER of the prescribed lens P = + 1.5 D and `P = (1)/(f)`
`THEREFORE` Focal length of the lens `f = (1)/(P) = (1)/(+1.5 D) = + 0.67` m
As the power of the lens is +ve, the lens is a converging (convex) lens.
Discussion
203.

A student studies the properties of Acetic Acid in his school laboratory. Write two observations of the reaction that occurs when he adds a pinch of sodium bicarbonate powder to 5 ml acetic taken in a test tube.

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Solution :Two OBSERVATIONS are :
(i) A GAS with brisk EFFERVESCENCE is EVOLVED,
(II) Lime water turns milky when this gas is passed through it.
Discussion
204.

The focal length (f) of a spherical mirror of radius of curvature R is

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Solution :The distance between OPTICAL centre and principal FOCUS is called FOCAL LENGTH of a lens.
Discussion
205.

What changes do you notice ? Why ?

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SOLUTION :The TOY CAR is at rest before winding the key but the same toy gets ENERGY to move when the key attached to it is wound up.
Discussion
206.

Draw a ray diagram to show the refraction of a monochromatic ray through a prism when it suffers minimum deviation. How is the angle of emergence related to the angle of incidence in the position.

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ANSWER :ANGLE of emergence=angle of INCIDENCE.
Discussion
207.

Increase in the converging power of eye lens cause 'hypermetropia'.

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ANSWER :1
Discussion
208.

An atom bomb consists of a piece of fissile material whose mass is __________.

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SOLUTION :SUBCRITICAL
Discussion
209.

What is scattering of light ? Use this phenomenon to explain why (i) the sun appears reddish at sunrise, and (ii) the clear sky appears blue.

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Solution :SCATTERING of light is the phenomenon of spreading of light in all DIRECTIONS due to interplay of light with tiny particles like air molecules, dust particles, colloidal solutions etc.
(i) At the time of sunrise the sun is situated near the HORIZON. Light from sun THEREFORE covers a larger distance in the earth.s atmosphere before REACHING an observer.s eyes. During its passage through atmosphere blue light is mostly scattered away and so the sun appear reddish.
(ii) During day time light from sun is scattered from air molecules in all directions. The amount of scattering is more for blue light because its wavelength is less. Hence, the clear sky appears blue.
Discussion
210.

If |vecA + vecB| = |vecA - vecB|, then the angle between vecA and vecB will be

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`theta=0`
`theta=45^(@)`
`theta=90^(@)`
`theta=180^(@)`

SOLUTION :`|vecA+VECB|=|vecA- vecB|`
S.B.S.
`|vecA+vecB|^(2)=|vecA-vecB|^(2)`
`(vecA+vecB)*(vecA+vecB)=(vecA-vecB)*(vecA-vecB)`
`THEREFORE theta=90^(@)`
Discussion
211.

Draw formation of images by a convex lens when the object is placed at infinity.

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SOLUTION :
Discussion
212.

State Newton's second law.

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Solution :The FORCE acting on a BODY is directly PROPORTIONAL to the rate of change of linear MOMENTUM of the body and the change in momentum TAKES place in the direction of the force.
Discussion
213.

Assertion: The change in air pressure affects the speed of sound. Reason: The speed of sound in a gas is proportional to the square of the pressure

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ANSWER :ASSERTION is FALSE, but the REASON is TRUE.
Discussion
214.

What is commercial unit of electric energy ?

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SOLUTION :KILOWATT HOUR or KWH.
Discussion
215.

Name the type of mirror used in the following situations. (a) Head lights of a car.(b) Side/rear view mirror of a vehicle.(c ) Solar furnace. Support your answer with reason.

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Solution :(a) Concave mirror : This is because concave mirror can produce powerful parallel beam of light when the light source is PLACED at their principal FOCUS.
(b) CONVEX mirror : This is because of its LARGEST field of view.
(c ) Concave mirror : This is because it concentrates the parallel rays of SUN at principal focus.
Discussion
216.

Image of an object held at near point N is formed at the back of retina of an eye, as shown in (Fig. 2.25). What is this defect of vision called ?

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SOLUTION :This DEFECT of vision is called hypermetropia of LONG sightedness.
Discussion
217.

Reena is a student of Class X of a Government School. She is a member of "Eco club" of her school. Answer the following questions based on the above information: (i) What suggestions would you like to give Reena to improve the environment in her school? (ii) What values are promoted by Reena?

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Solution :(i) (a) Growing plants and trees in the OPEN area in the school.
(b) Arrangement for water harvesting.
(C) Reporting any KIND of water leakage in the school.
(II) Environmental protection.
Discussion
218.

From a point on the ground a particle is projected with initial velocity u, such that its horizontal range is maximum. The magnitude of average velocity during its ascent is

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SOLUTION :Velocity of projection = u .
Range is maximum `rArr THETA = 45^(@)`
During time of ascent `rArr ` when H = `h_(mas)`
`rArru_(x) = u _(x) = u * cos theta`
Average velocity, `V_(A) = sqrt(V_(x)^(2) + V_(y)^(2))`
`V_(x)`= Average velocity along x-axis
` = (u* cos theta + u cos theta)/(2)`
`v_(x) = u * cos theta = u * 45^(@) = u //sqrt(2)to (1)`
Average velocity along y-axis `= (u_(y) + v_(y))/(2)`
`u_(y) = u sin theta = u // sqrt(2), v_(y) = 0 (at h_(max))`
`:. v_(y) = (u//sqrt(2))/(2) = (u)/(2sqrt(2)) rarr (2)` Average velocity during time of ascent
`sqrt((u/(sqrt(2)))^(2)+((u)/(2sqrt(2)))^(2))`
Average velocity
`= sqrt(u^(2)/(2)+(u^(2))/(4 xx 2))=sqrt((4u^(2) + u^(2))/(8))=(usqrt(5))/(2sqrt(2))`
Discussion
219.

Why are geostationary satellites not useful for studies of polar regions ?

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SOLUTION :GEOSTATIONARY satellites have two distinct characteristics :
(1) Geostationary satellites are HEO satellites and are placed at 35780 km above the EARTH's surface.

(2) A geostationary satellite revolves in the equatorial plane of the earth, and thus, it can never FLY above the polar regions. Hence, geostationary satellites are not USEFUL for studies of polar regions.
Discussion
220.

Old age homes are increasing in India. Give reason.

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Solution :1. Lfactors like ignorance TOWARDS the PEOPLE with incurable diseases like AIDS, T.B., Leprosy, mental illness as well as old people leads to increase in old age homes.
2. NEW generation is becoming more MATERIALISTIC and they feel it a BURDEN to keep to parents with them.
3. Due to these reasons ,old age homes are infreasing in India.
Discussion
221.

The root mean square velocity of gas molecules is 10km//s. The gas is heated till its pressure becomes four times. The velocity of gas molecules will be

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<P>`10Km//s`
`20Km//s`
`40Km//s`
`80Km//s`

SOLUTION :`P ALPHAT`
Discussion
222.

Assertion (A): The stars twinkle in night but the planets do not twinkle. Reason (R) :The stars are much bigger in size than the planets.

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Both (A) and (R) are TRUE and (R) is CORRECT explanation of the assertion.
Both (A) and (R) are true but (R) is not the correct explaration of the assertion.
(4) is true but (R) is false.
(A) is false but (R) is true.

Solution :STARS twinkle because stars are situated MUCH FARTHER away from the observer.s eye as compared to the planets.
Discussion
223.

List three different categories of contraception methods.(b) Why has Government of India prohibited prenatal sex determination by law ? State its benefits in the long run.(c) Unsafe sexual act can lead to various infections. Name two bacterial and two viral infections caused due to unsafe sex.

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Solution : (i) Barrier method - Where physical barriers like condoms (worn over penis), diaphragm (used by females), cervical cap and copper-T (an IUCD) are used.
(ii) Chemical method - Spermicidal applications by women, vaginal pills or oral contraceptive pills (OCPS) are used. OCPs are hormonal preparations which alter the hormonal level in FEMALE body. Use of OCPs is not meant for males.
(iii) Surgical method – Portion of vas deferens in male (vasectomy) or portion of fallopian tube in females (tubectomy) is cut or ligated. This stops release of gametes, preventing fertilisation.
(b) Selective Medical Termination of Pregnancy (MTP) of female foetus using amniocentesis is the main reason behind decline female-male sex ratio in our country. This is because many sections of our society considered girl child as a burden. That is why Government of INDIA prohibited prenatal sex determination by law.
Its benefits in the long run:
• Generating awareness about girls being equal helping hands in the family income.
• Banning prenatal sex determination tests.
• Banning certain ill practices in our society like dowry system.
(c) Bacterial diseases transmitted through sexual contact :
(i) Gonorrhoea (ii) Syphilis
Viral diseases : (i) Warts (ii) HIV-AIDS
Discussion
224.

Draw the diagram of the arrangement of apparatus showing the reaction of zinc granules.with dilute sulphuric acid and testing hydrogen gas by burning and label the soap bubbles filled with hydrogen.

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SOLUTION :
Discussion
225.

How do you draw normal to a spherical mirror at a particular point?

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SOLUTION :Join that particular point to the CENTRE of CURVATURE of the MIRROR.
Discussion
226.

In India, the frequency of alternating current is ………………. .

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Solution :In India, the FREQUENCY of ALTERNATING current is `ul("50 Hzor 50 CYCLES per SECOND")`.
Discussion
227.

Draw a circuit diagram of an electric circuit containing a cell, a key, an ammeter, a resistor of 2Omega in series with a combination of two resistors [4Omega each] in parallel and a voltmeter across the parallel combination. Will the potential difference across the 2Omega resistor be the same as that across the parallel combination of 4Omega resistors? Give reason.

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SOLUTION :
In SERIES combination of resistors, voltage across each resistor will PROPORTIONAL to its resistance. Equivalent resistance of parallel combination of `4Omega` resistors is `2Omega`. HENCE the voltage drop across `2Omega` resistor and the parallel combination of `4Omega` resistors will be the same.
Discussion
228.

Red coloured light is used in traffic signals to indicate the vehicles to stop, beasuse compared to other colours red light

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has HIGH frequency
has LESS wavelength
scatters more
scatters less

Answer :D
Discussion
229.

Electric potential V and electric flux phi are

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both vectors
both scalars
V is SCALAR, `PHI` is VECTOR
V is vector, `phi` is scalar

Answer :B
Discussion
230.

The correct relation between current I and amount of charge flown q during a time t through a conductor is

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`I=qt`
`Q=I^2t`
`q=It`
`I=q^2/t`

SOLUTION :CORRECT relation is current `I= (TOTAL charg e flow q)/(Total time t) implies q=It`
Discussion
231.

An object of height 4 cm is placed at a distance of 30 cm from the optic centre of a convex lens of focal length 20 cm. Draw a ray diagram to find the position and size of the image formed. Mark the optic centre O and the principal focus F on the diagram. Also find the approximate ratio of the size of the image to the size of the object.

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SOLUTION :`{:("Convex lens","Object","image"),(f=+20 cm,h=+4 cm,h.=?),(r=2f=+40cm,u=-30 cm,v=?),(m=?,,):}`
Object is placed between F and `2F_(1)`
The ray diagram is drawn using appropriate scale of measurement.

`OF_(1)=OF_(2)=20 cm "" OC_(1)=OC_(2)=40 cm`
`OB = 30 cm "" AB=4cm`
`B.A.=8 cm`
Ratio of the size of the image to the size of the object.
Magnification `(m)=(v)/(u)=(h.)/(h)=((+60))/((-30))=-2`
Verification :
Using Lens formula `=(l)/(v)-(l)/(u)=(l)/(f)`
`(l)/(v)-(1)/((-30))=(1)/((20)), (l)/(v)=(1)/(20)-(1)/(30),(l)/(v)=(1)/(60), v=+60 cm`
• The image is formed at a distance of 60 cm on the RIGHT side of the convex lens. (+ve sign signifies this)
Magnification `(m)=(v)/(u)=(h.)/(h)`
`=((+60))/((-30))=(h.)/(4), -2=(h.)/(4), "" h.=-8cm`
• The image formed (h.) has a height of 8 cm which is more than object height (h). The image formed is enlarged.
• h. has a - ve sign which indicates that the image formed is REAL and inverted.
Discussion
232.

When resistors of resistances R_1 and R_2 (R_2 gt R_1) are connected in series and the currents flowing through them are I_1 and I_2respectively, then …………….. .

Answer»

`I_1 = I_2`
`I_1 GT I_2`
`I_1 LT I_2`
NOTHING can be SAID about the currents

Solution :`I_1 = I_2`
Discussion
233.

Who is the first Indian to travel to space?

Answer»

RAKESH Shanna
Kalpana Chawla
Sunita Williams
none of these

SOLUTION :(a) Rakesh SHARMA
Discussion
234.

Why do we have to bring a small object nearthe eye inorder to see it clearly?

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SOLUTION :1.The apparent size of an OBJECT DEPENDS on the angle subtended by the object at the eye.
2. When we bring a small object is seen CLEARLY.
Discussion
235.

How do we decide that a given material is a good conductor of electricity or is an insulator?

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Solution :1.Materials that offer very large resistance to the flow of electric current are CLASSIFIED as insulators. Hence, electric current cannot flow FREELY through them. Their atoms hold on to their electrons TIGHTLY. E.g.Glass.
2. Materials that offer very low resistance to the flow of electric current are termed as conductors. Here electric current can flow freely. E.g.Metals like copper. Conductor implies that the outer electrons of the atoms are loosely bound and free to move through the MATERIAL.
Discussion
236.

Thickness of insulated copper wire used in ihe primary turns and secondary turns ofa transformer are not equal. In a step up transformer which set of turns (primary/secondary) is made of thicker copper wire? Justify your answer.

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ANSWER :PRIMARY
Discussion
237.

Thickness of insulated copper wire used in ihe primary turns and secondary turns ofa transformer are not equal. Write down the working principle of transformer.

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ANSWER :MUTUAL INDUCTION.
Discussion
238.

(a) Name the gaseous plant hormone. Describe its three different actions in plants. (b) Which hormone is known as stress hormone in plants ? Why?

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Solution :Abscisic acid is KNOWN as STRESS HORMONE. It increases the tolerance of plants to VARIOUS kinds of stress. (Eg. During WATER stress and drought conditions. Abscisic acid causes stomatal closure.
Discussion
239.

Two resistors X and Y of resistances 2 omega and 3 omega respectively are first joined in parallel and then in series. In each case the voltage supplied is 5 V. (i) Draw circuit diagrams to show the combination of resistors in each case. (ii) Calculate the voltage across the 3 Q resistor in the series combination of resistors.

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Solution :(i) APPROPRIATE circuit diagrams are drawn below

(zz) Total resistance of circuit in SERIES arrangement
R = X + Y = 2 + 3 = 5 `omega`
`therefore`Circuit CURRENT`I=(V )/(R )=(5V)/(5 omega)=1 A`
`therefore` Voltage across the 3`omega` resistor, `V_(y) = I xx Y = 1 A xx3 omega = 3V`.
Discussion
240.

If is found that| vec A+vec B| = |vec A|. This necessarily implies.

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` VEC B= 0`
`vec A, vec B` are ANTIPARALLEL
` vec A, vec B` are perpendicular
Both A and B

Answer :D
Discussion
241.

It follows from Question 34, that the velocity in case of (b) is

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more than the VELOCITY in CASE of (a)
LESS than the velocity in case of (a)
equal to the velocity in case of (a)
SQUARE of the velocity in case of (a)

Answer :B
Discussion
242.

In India, domestic circuits are supplied with frequency of. . . . . . . . .. .

Answer»

60 Hz
50 Hz
220 Hz
230 Hz

Answer :B
Discussion
243.

Express the power of concave lens of focal length 20 cm .

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Solution :Given : focal length = 20 CM
To FIND : Power of lens
Solution : P = `- 1/(f(in meter)) `
` P = 1/(-0.2)`
P `= -5` D.
`therefore` Power of lens = -5 Diopter
Discussion
244.

What change in the deflection of the compass needle placed at a point near current carrying straight conductor shall be observed if the (a) current through the conductor is increased? (b) direction of current in the conductor is reversed? (c ) compass is moved away from the conductor?

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Solution :(a) DEFLECTION increases.
(B) Direction of deflection is reversed.
(C ) Deflection DECREASES.
Discussion
245.

Which of the following cannot be speed (v) - time (t) graph?

Answer»




ANSWER :C
Discussion
246.

Whichtype of connection is done for electricappliances ?

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SOLUTION :PARALLEL
Discussion
247.

(a) Identify A, B and C in the given diagram and write their functions. (b) Mention the role of gamete and zygote in sexually reproducing organisms.

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Solution :
(a) A - STIGMA. The TOP PART of carpel is called stigma. Stigma is for receiving the pollen grains from the anther of stamen during pollination.
B - Pollen tube. When a pollen grain falls on the stigma, it bursts open and grows a pollen tube downward through the style towards the female gamete in the ovary. A male gamete moves down the pollen tube.
C- Female gamete (OVUM).It is a special reproductive female sex cell which combines with male gamete to form zygote.
(b) Sexual reproductiontakes place by the combination of special reproductive cells called sex cells. These cells are of two types - male sex cells and female sex cells, which are coming from two different parents-a male and a female. The cells involved in sexual reproduction are called gametes. In sexual reproduction, a male gamete fuses with a female gamete to form a new cell called zygote. This zygote then grows and develops into a new organism in due courseof time.
Discussion
248.

A calorimeter has mass 100 g and specific heat 0.1 kcal/ kg^@C. It contains 250 gm of liquid at 30^@C having specific heat of 0.4 kca/kg^@C. If we drop a piece of ice of mass 10g at 0^@C, what will be the temperature of the mixture?

Answer»

Solution :Given : Mass of calorimeter `(m_1)` = 100 g, Specific heat `(c_1) = 0.1 KCAL//kg ^@C`, Temperature `(t_1)=30^@C`, Mass of liquid `(m_2)`=250 g , Specific heat `(c_2) = 0.4 kcal//kg^@ C`, Temperature `(t_2)=30^@C`, Mass of Ice `(m_3)` = 10 g , Specific heat `(c_3) = 0.5 kcal//kg^@C`, Temperature `(t_3)=0^@C`
To Find :Final Temperature (T)
Solution : Converting GRAMS into calories ,
1 g = 7.716 cal
100 g =771.6 cal = 0.7716kcal
250 g = 1929 cal =1.929 kcal
10 g = 77.16 cal =0.07716 kcal
Heat capacity of water = 1 kcal/kg
Latent heat of fusion of ice = 80 kcal/kg
Heat gained or lost= mass X heat capacity x change in temperature
Since, ice is put in the liquid, there is heat loss : Change in temperature = (30-T)
Heat lost by calorimeter and liquid = heat gained by ice
Substituting , [(30-T)0.7716 x 0.1] + [(30-T)1.926 x 0.4 ]
= (0.07716 x 80 ) + T x 0.07716 x 1
`therefore ` 2.3148 - 0.07716 T + 23.112 - 0.7704 T = 6.1728 + 0.07716 T
`therefore` 0.92472 T = 19.254
`therefore T=20.82^@C`
Final temperature of the mixture will be `20.82^@C`
Discussion
249.

A truck of mass 1000 kg accelerates uniformly from rest to a velocity of 15ms^(-1) in 5 seconds. Calculate (i) its acceleration, (i) its gain in K.E., (iii) average power of the engine during this period, neglect friction.

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SOLUTION :(i)`a=(v-u)/t=3m//s^(2)`
(II)Gain in K.E.`=1/2m(v^(2)-u^(2))=1.125xx10^(5)J`
(iii) `P=W/t=22500W`
Discussion
250.

Two lamps, one rated 100 Wat 220 V, and the other 60 W at 220 V, are connected in parallel to electric mains supply. What current is drawn from the line if the supply voltage is 220 V?

Answer»

Solution :Given: LAMPS are connected in PARALLEL
Potential difference = 220 V
Power of one lamp `P_1` = 100 W
Power of second lamp `P_2` = 60 W
To find : Current (I)
Formula : P =VI
Solution : Since, both the lamps are connected in parallel their potential difference will be equal.
We know, P =VI or , I=P/V
`I_1=P_1/V ` and `I_2=P_2 /V `
Thus, TOTAL current through the circuit is I=`I_1+I_2`
`therefore I=P_1 /V + P_2 /V`
`therefore I="100 W"/"200 V"+"60 W"/"200 V"`
`=(100+60)/220 =160/220`
I=0.727 A
`therefore ` Current is equal to 0.73 A
Discussion