ELECTRICITY

CHAPTER – 11: ELECTRICITY

VOLUME – 1

Section A: Multiple Choice Questions (1 Mark Each)

1. Which device is used to measure electric current in a circuit?
   
   a) Voltmeter
   
   b) Ammeter
   
   c) Galvanometer
   
   d) Thermometer
   
   ANS: b) Ammeter
2. In which arrangement do resistors give minimum resistance?
   
   a) Series
   
   b) Parallel
   
   c) Both a and b
   
   d) None
   
   ANS: b) Parallel
3. What is the SI unit of electric charge?
   
   a) Volt
   
   b) Ampere
   
   c) Coulomb
   
   d) Ohm
   
   ANS: c) Coulomb
4. Which of the following represents Ohm’s Law?
   
   a) \( V = IR \)
   
   b) \( P = VI \)
   
   c) \( I = Rt \)
   
   d) \( Q = It \)
   
   ANS: a) \( V = IR \)
5. Which material is used in the filament of electric bulbs?
   
   a) Copper
   
   b) Aluminium
   
   c) Tungsten
   
   d) Nichrome
   
   ANS: c) Tungsten
6. A wire has resistance R. If it is stretched to double its length, cross sectional area reduced to half. What will be the new resistance?
   
   a) R/2
   
   b) 2R
   
   c) 4R
   
   d) R
   
   ANS: c) 4R
7. Fuse is always connected in –
   
   a) Parallel
   
   b) Series
   
   c) Diagonal
   
   d) None
   
   ANS: b) Series
8. Electric power is equal to –
   
   a) I/R
   
   b) \( IR^2 \)
   
   c) \( V \times I \)
   
   d) V/I
   
   ANS: c) \( V \times I \)
9. A current of 1 A flows through a wire for 10 seconds. How much charge flows?
   
   a) 10 C
   
   b) 5 C
   
   c) 1 C
   
   d) 100 C
   
   ANS: a) 10 C
10. Which device works on heating effect of current?
    
    a) Fan
    
    b) Bulb
    
    c) Battery
    
    d) Switch
    
    ANS: b) Bulb

Assertion-Reason Questions

11. Assertion: In a parallel circuit, total resistance decreases.
    
    Reason: Current divides through each resistor.
    
    Correct option: a) Both A and R are true, and R is the correct explanation.
12. Assertion: Copper is used for household wiring.
    
    Reason: It has low resistivity and is a good conductor.
    
    Correct option: a) Both A and R are true, and R is the correct explanation.

Section B: Short Answer Questions (2 Marks Each)

13. Why is tungsten used in electric bulbs?
    
    ANS: High melting point and glows without melting.
14. Define 1 volt. Write relation between work and charge.
    
    ANS: 1V = 1J/1C; \( V = W/Q \).
15. State two factors affecting resistance of a conductor.
    
    ANS: Length and cross-sectional area.
16. Why is parallel connection preferred in household circuits?
    
    ANS: Same voltage across devices and independent operation.
17. State two disadvantages of series circuits.
    
    ANS: One device failure stops entire circuit; voltage divides.

Section D: Short Answer Questions (3 Marks Each)

18. In the given circuit calculate the (i) equivalent resistance ii) current iii) power consumed in watts in the resistor of 2Ω :
    
    
    
    ANS:
    
    Equivalent resistance = \( R_1 + R_2 = 1 \Omega + 2 \Omega = 3 \Omega \)
    
    \( I = V / R = 6 V / 3 \Omega = 2 \text{ A} \)
    
    Electric power, \( P = I^2 \times R = (2 \text{ A})^2 \times 2 \Omega = 4 \times 2 \text{ W} = 8 \text{ W} \)
19. A bulb is rated 60W, 220V. Calculate: (a) Current (b) Resistance
    
    ANS:
    
    \( I = P/V = 60/220 \approx 0.27 \text{ A} \)
    
    \( R = V/I = 220/0.27 \approx 814.8 \Omega \)
20. How is the resistivity of alloys compared with those of pure metals from which they may have been formed?
    
    OR
    
    If the conductor A is made of copper and the conductor C is made of constantan (alloy of copper and nickel), then which one of the two will have more electrical resistance and why?
    
    ANS:
    
    Resistivity of alloys is generally higher than its constituent metals. Therefore, alloy has more resistance.
21. Show how you would connect three resistors each of resistance 6 Ω, so that the combination has a resistance of 9 Ω. Also justify your answer.
    
    ANS: Connect two in parallel (\( \frac{1}{6} + \frac{1}{6} = \frac{2}{6} \Rightarrow R_p = 3 \Omega \)) and one in series (\( 3 \Omega + 6 \Omega = 9 \Omega \)).
22. State Joule’s Law of heating and give two uses.
    
    ANS: \( H = I^2Rt \). Uses: Electric heater, iron.

Section E: Long Answer Questions (5 Marks Each)

23. (i) How is electric current related to the potential difference across the terminals of a conductor?
    
    (ii) Why should an ammeter have low resistance?
    
    (iii) Two V-I graphs A and B for series and parallel combinations of two resistors are as shown. Giving reason state which graph shows (a) series, (b) parallel combination of the resistors.
    
    
    
    ANS:
    
    (i) \( V=IR \)
    
    (ii) To measure the entire current passing through the circuit, the ammeter should have low resistance.
    
    (iii) Series: \( R_s = R_1 + R_2 \) (Maximum resistance). Parallel: \( R_p \) (Minimum resistance). Since slope of I-V graph represents 1/R (or V-I represents R, assuming V on y-axis graph B has higher slope/resistance, A has lower).
    
    Note: Based on standard V-I graph where V is x-axis and I is y-axis, Slope = I/V = 1/R. Higher slope means lower resistance. So B (higher slope) is Parallel, A (lower slope) is Series. If V is y-axis, B is Series.
    
    From text: So, \( R_A > R_B \) (This implies graph A corresponds to higher resistance/Series if V is y-axis).
24. What is a fuse? Why is it necessary? Write 2 precautions & 1 use.
    
    ANS: Fuse protects from overload by melting. Precautions: Use correct rating, switch off supply before changing. Use: In home main circuits.
25. A fuse wire melts at 5 A. If it is desired that the fuse wire of same material melt at 10 A, then whether the new fuse wire should be of smaller or larger radius than the earlier one? Give reasons for your answer.
    
    ANS:
    
    Let the resistance of the wire be R, heat produced \( H \propto I^2R \).
    
    To prevent melting at higher current, resistance must be lower (or heat dissipation capacity higher).
    
    \( R \propto \frac{1}{A} \propto \frac{1}{r^2} \).
    
    So, at 10A, the new fuse wire of same material and length needs a larger radius than the earlier one to handle more current without melting immediately.

Section E: Case Based Study (4 Marks Each)

26. Riya is studying household circuits. She observed that when multiple appliances like fans, lights, and TV are used in her house, all of them work independently and receive equal brightness or speed.
    
    1) Which bulb glows brighter? 100W or lower? (Assuming implied context).
    
    2) Why are bulbs connected in parallel?
    
    3) What is the Voltage across each bulb? Will both work if one fails?
    
    ANS:
    
    1) 100W (in parallel, P is proportional to rating).
    
    2) To get full voltage and work independently.
    
    3) 220V. Yes, because connected in parallel.
27. Raj wanted to test how much electricity his iron box consumes. He checked the label which read ‘220V, 1000W’. He connected it to a power supply…
    
    1) What is the Power consumed?
    
    ANS: \( P = V \times I = 220 \times 5 = 1100 \text{ W} \) (Note: Text says 1000W label, calculation uses 5A current. \( 220 \times 5 = 1100 \)).
    
    2) What is the Function of fuse?
    
    ANS: Breaks circuit when current exceeds limit.
    
    3) What if higher-rated fuse used? Which effect of current is used?
    
    ANS: Won’t melt \( \rightarrow \) appliance damage/fire risk. Heating effect.