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Q. 11. Draw a schematic diagram of an electric circuit consisting of a battery of five 2 V cells, a 20  resistor, a 30  resistor, a plug key, all connected in series. Calculate the value of current flowing through the 20  resistor and the power consumed by the 30  resistor. 3

Ans. R1 = 20  R2 = 30
Resultant resistance, R = R1 + R2 = 20 + 30 = 50
Total potential difference, V = 5 X2 = 10 volts
Current, I = ?
By Ohm’s Law,
V = I R
I =
Since current remains constant in  a series.
I = I1 + I2
∴ The current flowing through
20 resistor is also 0·2 A.
Power consumed by 30 resistor,
P2 = V2I2
I2 = 0·2 A     R2 = 30     V2 = ?
V2 = I2R2 = 0·2 X  = 6 volts  P2 = 6 X 0·2 = 1·2 W

Q. 12. What is ethanol? Draw the structure of ethanol molecule. How does ethanol behave with the following :
(a) Sodium
(b) Excess of conc. sulphuric acid at 443 K
Write chemical equation for each reaction. 3

Ans.

• Ethanol is the second member of the homologous series of alcohol. It’s formula is C2H5OH. It is the most widely used alcohol. It’s common name is ethyl alcohol.
• Structure formula
  
• Ethanol reacts with sodium to form sodium ethoxide and hydrogen gas
  

• When ethanol is heated with excess of conc. sulphuric acid at 443 K, it gets dehydrated to form ethene
    

Science 2009 Question Papers Class X
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