## 04 April 2015

### Solved Electricity numerical for class 10

1. Question: Two bulbs have ratings 100 W, 220 V and 60 W, 220 V respectively. Which one has a greater resistance?

Answer: P=VI=  V2/R For the same V, R is inversely proportional to P.

Therefore, the bulb 60 W, 220 V has a greater resistance.

2. Question: A torch bulb has a resistance of Ω when cold. It draws a current of 0.2 A from a source of 2 V and glows. Calculate
(i) the resistance of the bulb when glowing and
(ii) explain the reason for the difference in resistance.

Answer:
(i) When the bulb glows:

V = I R ---- Ohm's law R = V/I = 2/.2 =10 Ω

(ii) Resistance of the filament of the bulb increases with increase in temperature. Hence when it glows its resistances is greater than when it is cold.

3. Question: Calculate the resistance of 1 km long copper wire of radius 1 mm. (Resistivity of copper = 1.72 x 1 0-8

Answer: L = 1 km = 1000 m
R = 1 mm = 1 x 1 0-3
p = 1.72 x 1 0-8  W m

Area of cross section = p r2  = 3.14 x 1 0-3 x 1 0-3 =  3.14 x 1 0-6

R = pl/A = (1.72 x 1 0-8  x 1000 ) / 3.14 x 1 0-6  = 5.5 W

4. Question: When a potential difference of 2 V is applied across the ends of a wire of 5 m length, a current of 1 A is found to flow through it. Calculate:
(i) the resistance per unit length of the wire
(ii) the resistance of 2 m length of this wire
(iii) the resistance across the ends of the wire if it is doubled on itself.

Answer: (i) V = I R ----- Ohm's law R=V/I=2/1= 2 Ohm

Resistance per unit length: 2/5= 0.4 Ohm/m

(ii) Resistance of 2 m length of the wire = 0.4 x 2=0.8 ohm

(iii) When the wire is doubled on itself:

(a) the area of cross-section is doubled. If A is the original C.S. area, now it is 2 A.

(b) The length becomes half i.e.L/2

Resistance of this wire =R' = p (l/2)/(2A) = 1/4(p(L/A)

But p(L/A) = 2 ohm

R' = 1/4 x 2=0.5 Ohm

5. How much work is done in moving 4 C across two point having pd. 10 v

Solution : W = VQ = 10 x 4 = 40J

6. How much energy is given to each coulomb of charge passing through a 9 v battery?

Solution:  Potential difference = Work done = Potential difference × charge

Where, Charge = 1 C and Potential difference = 6 V

Work done = 9×1 = 9 Joule.

7. 100  j of work is done in moving a charge of 5 C from one terminal of battery to another . What is the potential difference of battery?

Solution: V = W/Q =  100j/5C = 20 V

8. If 4 x 10 -3 J of work is done in moving  a particles carrying a charge   of 16 x 10 - 6 C from infinity to point P .What will be the potential at a point?

Solution: the potential at a point is work done to carry unit from one point to another
= (4 x 10 -3 ) /(16 x 10 - 6 C) = 250 V

9. Calculate the current and resistance of a 100 W ,200V electric bulb.

Solution:Power,P = 100W   and     Voltage,V = 200V

Power  P  = VI
So, Current I = P/v = 100/200 = 0.5A

Resistance R = V/I = 200/0.5 = 400W.

10.Calculate the power rating of the heater coil when used on 220V supply taking 5 Amps.

Solution:

Voltage ,V = 220V     and  Current ,I = 5A,

Power,P = VI = 220 × 5 = 1100W = 1.1 KW.

11.A lamp can work on a 50 volt mains taking 2 amps.What value of the resistance must be connected in series with it so that it can be operated from 200 volt mains giving the same power.

Solution: Lamp voltage ,V = 50V and  Current ,I = 2 amps.

Resistance of the lamp = V/I   = 50 / 2     = 25 Ω

Resistance connected in series with lamp = r.
Supply voltage = 200 volt. and  Circuit current I = 2 A

Total resistance Rt= V/I  = 200/2    = 100Ω
Rt = R + r          =>    100 = 25 + r      =>  r = 75Ω

12. Calculate the work done in moving a charge of 5 coulombs from a point at a potential of 210 volts to another point at 240 volts

Solution: Potential diffrence  = 210 ­ - 240 = ­30 V

So, W.= V x  Q = ­30V  x  5C = ­150 Joules

13. How many electrons pass through a lamp in one minute if the current be 220 mA?

Solution:

I  = 220 mA = 0.22 A

I = Q/T

0.22 = Q/60

Q= 0.22 x 60 = 13.2 C

No of electron carry 1 C charge = 6 x 10 18

No of electron carry 13.2 C charge = 6 x 10 18 x 13.2 C = 79.2 x 10 18

14.Calculate the current supplied by a cell if the amount of charge passing through the cell in 4 seconds is 12 C ?

Solution:

I = Q/t = 12/4 = 3A

15. A 2 Volt cell is connected to a 1 Ω resistor. How many electrons come out of the negative terminal of the cell in 2 minutes?

Solution: V = IR =>  I = V/R = 2/1 = 2 A

I = Q/t  =>  Q = It = 2 x 2 x 20 = 80 C

No of electron carry 1 C charge = 6 x 10 18

No of electron carry  80 C  charge = 6 x 10 18 x 80 C = 108  x 10 18   = 1. 08  x 10 20

16. (a) How much current will an electric bulb draw from a 220 V source, if the resistance of the bulb filament is 1200 Ω?

(b) How much current will an electric heater coil draw from a 220 V source, if the resistance of the heater coil is 100 Ω?

Solution

(a) We are given V = 220 V; R = 1200 Ω.
we have the current I = V/R  = 220 V/1200 Ω = 0.18 A.
(b) We are given, V = 220 V, R = 100 Ω.
we have the current I = V/R =  220 V/100 Ω = 2.2 A.

17. The potential difference between the terminals of an electric heater is 60 V when it draws a current of 4 A from the source. What current will the heater draw if the potential difference is increased to 120 V?

Solution

We are given, potential difference V = 60 V, current I = 4 A.

According to Ohm’s law, R = V/I = 60/4 =15Ω

When the potential difference is increased to 120 V

the current is given by current = V/R = 120V/15 = 8A

The current through the heater becomes 8 A.

18. A 4 Ω resistance wire is doubled on it. Calculate the new resistance of the wire.

Solution

We are given, R = 4 Ω.

When a wire is doubled on it, its length would become half and area of cross-section would double. T
So,  a wire of length l and area of cross-section A becomes of length l/2 and area of cross section 2A. we have R = ρ(l/A)

R1 = ρ((l/A) / 2A)   where R1 is the new resistance.

Therefore, R1/R = ρ((l/A)/2A) / ρ(l/A) = 1/4

Or, R1 = R/4 = 4Ω/4 = 1Ω

The new resistance of the wire is 1 Ω.

19 . 3.A circuit is made of 0.4 Ω wire,a 150Ω bulb and a 120Ω rheostat connected inseries.Determine the total resistance of the resistance of the circuit.

Solution: Resistance of the wire = 0.4Ω
Resistance of bulb = 150Ω
Resistance of rheostat = 120Ω
In series,  Total resistance ,R = 0.4 + 150 +120 = 270.4Ω

20. A current of 0.2 Ampere flows through a conductor of resistance 4.5 Ω. Calculate the potential difference at the ends of the conductor.

Solution:

The potential difference at the ends of the conductor. =  V = IR = 0.2  x  4.5  = 0.9 V

21. A lamp has a resistance of 96 ohms. How much current flows through the lamp when it is connected to 120 volts?

Solution: I = V/R = 120/96 = 1.25 A [V = IR]

The current through the lamp equals 1.25 A.'

22. The manufacturer specifies that a certain lamp will allow 0.8 ampere of current when 120 volts is applied to it. RRWhat is the resistance of the lamp?

Solution: V = IR So, R = V/I = 120/0.8 = 150 W

23. How much voltage is required to cause 1.6 amperes in a device that has 30 ohms of resistance?
Given: V = IR = 1.6 x 30 = 48 V

24. How much power is dissipated when 0.2 ampere of current flows through a 100-ohm resistor?
Ans: P = V I = IR x I = I2 R = 0.2 x 0.2 x 100 = 4 W

25, How much energy is converted by a device that draws 1.5 amperes from a 12-volt battery for 2 hours?

W = Pt, P = V I So, W = VIt = 12 x 1.5 x 2 = 36 Wh

#### 23 comments:

1. This comment has been removed by a blog administrator.

2. please upload solution of unsolved questions

1. all unsolved question of science in learncbse.in class8 9 10 11 12

3. SAT and ACT both are very popular and have equal importance and result. And all free sat prep classes in nyc colleges and universities accept both these. And we know SAT TEST is long term process but very important. How we can get good composite scores.

4. Interesting blog. This is one of my favorite blog also I want you to update more post like this. Thanks for sharing this article.
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5. its a gr8 blog but pls do correct the confusion in 13th qs about value of current given as 200mA and 220mA

6. Its not a great blog the ques are so low level
Even for amateur

7. Thanks for sharing useful information regarding CBSE Exams. You have really shared some quality news and interesting information regarding CBSE 10th Results 2015 with us. Thanks for the useful information. cbseresults.nic.in is the official website of Central Board of Secondary Education. I wish best of luck to all the students who is waiting for CBSE Results.

8. check question 15 it should be 60 in place of 20

1. yea u r right because a minute have 60 seconds not 20

blog administrator. kindly change it

:D

9. It was really helpful thanks.

10. mijhay 1oth class ka 1st chpter ka numerical solved snd kro

11. Very nice post, impressive. its quite different from other posts. Thanks for sharing.

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12. Pls solve this for me. You have two metallic wires each of 6 ohm and 3 ohm. How will u connect these wires to get the effective resistance of 2 ohm

1. Parallel combination

2. Parallel combination

13. mujhe reproduction chapter ke notes send kar do

14. Sir,
I want to know why r u taking 6.0×10^18 n not the charge of electrons1.67×10^-19 electrons..

15. i think u r talking about question number 13,15
it is given that :
Number of electron carry 1 C charge ,
not the charge of an electron

16. In q9 its given resistance=400w The unit is not watt its ohm

(JUST A MINUTE MISTANKE BUT LARGE IN THERMS OF PHYSICS)

17. Hi
How did u do SEO for this blog?