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Q1. Current through 10Ω resistor connected to 12V is
Using Ohm’s law, I = V/R = 12V / 10Ω = 1.2A. A current of 1.2 amperes flows through the 10Ω resistor. This is a direct application of Ohm’s law.
Q2. Joule’s law applies to
Joule’s law of heating (H = I²Rt) applies to resistive circuits where electrical energy is converted into heat energy. It is valid for both series and parallel circuits as long as there is resistance present. It does not apply to magnetic circuits.
Q3. In a parallel circuit, total current is high because
In a parallel circuit, the total resistance is low because there are multiple paths for current. Since I = V/R, lower resistance means higher current. This is why parallel circuits draw more total current than series circuits.
Q4. If one branch in a parallel circuit breaks, the remaining circuit
If one branch in a parallel circuit breaks, the remaining branches continue to work normally. This is because the other branches still provide paths for current. This independent operation is a major advantage of parallel circuits.
Q5. Joule’s law is used in calculations when
Joule’s law (H = I²Rt) can be expressed in different forms using Ohm’s law: H = VIt, H = V²t/R, or H = I²Rt. When appliance voltage is known, the formula H = V²t/R is often used.
Q6. Using Ohm’s law, heat produced can be written as
Joule’s law states that heat produced is H = I²Rt, where I is current, R is resistance, and t is time. Using Ohm’s law (V = IR), this can also be written as H = VIt or H = V²t/R.
Q7. For three resistors in parallel, the relation between currents is
In a parallel circuit, the total current is the sum of the currents in the individual branches: I = I1 + I2 + I3. This follows from Kirchhoff’s Current Law.
Q8. In a parallel combination, the potential difference across each resistor is
In a parallel combination, the potential difference (voltage) across each resistor is the same. All resistors are connected directly across the source, so each experiences the full voltage.
Q9. Equivalent resistance of resistors in parallel is denoted by
The equivalent resistance of resistors in parallel is denoted by Rp. For series, it is denoted by Rs. The subscript ‘p’ stands for parallel, and ‘s’ stands for series.
Q10. Equivalent resistance of a parallel circuit is always
The equivalent resistance of a parallel circuit is always less than the smallest individual resistance. This is because adding parallel paths reduces the overall resistance.
Q11. In a purely resistive circuit, electrical energy is converted entirely into
In a purely resistive circuit, electrical energy is converted entirely into heat energy. This is called Joule heating. This principle is used in electric heaters, irons, toasters, and other heating appliances.
Q12. If 12V is applied across 18Ω, current is
Using Ohm’s law, I = V/R = 12V / 18Ω = 0.67A (rounded). So a current of about 0.67 amperes flows through the 18Ω resistor.
Q13. In a parallel circuit, resistors are connected
In a parallel circuit, resistors are connected at the same two points (common nodes). This means each resistor has the same potential difference across it. They provide multiple paths for current.
Q14. In parallel circuits, equivalent resistance decreases because
In parallel circuits, the effective cross-sectional area for current flow increases because current has multiple paths. According to R ∝ 1/A, an increase in effective area causes resistance to decrease.
Q15. Electric irons work on the principle of
Electric irons work on the principle of the heating effect of electric current. The heating element (nichrome wire) converts electrical energy into heat, which is used to iron clothes.
Q16. According to Joule’s law, heat produced is proportional to
According to Joule’s law, heat produced is directly proportional to time (H ∝ t). It is also proportional to the square of current (I²) and resistance (R). So H = I²Rt.
Q17. Joule’s law of heating states that heat produced is proportional to
Joule’s law states that heat produced in a resistor is proportional to the square of the current (I²), the resistance (R), and the time (t): H ∝ I²Rt. This means if current doubles, heat increases four times.
Q18. The expression H = I²Rt shows heat depends on
The expression H = I²Rt shows that the heat produced depends on current (I), resistance (R), and time (t). This is Joule’s law of heating.
Q19. Three resistors of 30Ω, 20Ω and 60Ω in parallel give equivalent resistance
For parallel combination: 1/Rp = 1/30 + 1/20 + 1/60 = 2/60 + 3/60 + 1/60 = 6/60 = 1/10. So Rp = 10Ω. The equivalent resistance is 10Ω.
Q20. Heat produced in a resistor in time t is
Heat produced in a resistor is H = VIt (using V = IR, this becomes H = I²Rt). This is Joule’s law. The heat energy is the product of voltage, current, and time.
Q21. The unit of heat energy produced is
The unit of heat energy produced is the joule (J). It is the same unit as work and energy. In some contexts, heat energy is also measured in calories (1 cal = 4.186 J).
Q22. In series circuit, power consumed by each resistor depends on
In a series circuit, the current through each resistor is the same. The power consumed by each resistor is P = I²R, so since I is the same, power depends on the resistance of each resistor.
Q23. In heating devices, electrical energy is mainly converted into
In heating devices like electric irons, heaters, and toasters, electrical energy is mainly converted into heat energy. This is due to the heating effect of electric current.
Q24. One major disadvantage of series circuit is
One major disadvantage of a series circuit is that if one component fails, the entire circuit stops working. This is because there is only one path for current flow. This is why series circuits are not used in household wiring.
Q25. Series circuits are impractical for household appliances because
Series circuits are impractical for household appliances because different devices require different currents to operate properly. In a series circuit, the same current flows through all devices, which would not work for appliances with different power ratings.
Q26. In a parallel circuit, the total current is equal to
In a parallel circuit, the total current is equal to the sum of the currents in the individual branches: Itotal = I1 + I2 + I3 + … . This is based on Kirchhoff’s Current Law.
Q27. According to parallel combination rule
The rule for parallel combination is 1/Rp = 1/R1 + 1/R2 + 1/R3 + … . This formula gives the reciprocal of the equivalent resistance.
Q28. Parallel circuits are safer for homes because
Parallel circuits are safer for homes because each appliance functions independently. If one appliance fails or is switched off, others continue to work. Also, each appliance gets the full voltage.
Q29. In household wiring, appliances are connected in
In household wiring, appliances are connected in parallel. This ensures each appliance gets the full 220V supply and can be operated independently. This is the safest and most practical arrangement.
Q30. Current through 30Ω resistor connected to 12V is
Using Ohm’s law, I = V/R = 12V / 30Ω = 0.4A. So a current of 0.4 amperes flows through the 30Ω resistor.
Q31. Parallel circuits are preferred because they provide
Parallel circuits are preferred because they provide independent operation of appliances. Each appliance can be switched on or off without affecting others. This is why household wiring uses parallel connections.
Q32. Heating effect is used in
The heating effect of electric current is used in electric heaters, irons, toasters, and other heating appliances. Generators, motors, and fans use other principles (electromagnetic induction and mechanical motion).
Q33. Heat produced increases when resistance is
According to Joule’s law, H = I²Rt. If resistance increases (and current is kept constant), heat produced increases. This is why heating elements have high resistance.
Q34. Joule’s law is valid only when current is
Joule’s law H = I²Rt is valid for steady (direct) current. For alternating current, the effective (RMS) value of current is used. The law holds for both AC and DC when the appropriate current values are used.
Q35. In parallel circuit, power consumed depends on
In a parallel circuit, the voltage across each resistor is the same (battery voltage). Power consumed is P = V²/R, so power depends on the resistance of each branch.
Q36. The power supplied to a circuit is given by
The power supplied to a circuit is given by P = VI, where V is the voltage and I is the current. Using Ohm’s law, this can also be written as P = I²R or P = V²/R.
Q37. Heating effect of current is an example of conversion of
The heating effect of current is an example of the conversion of electrical energy to heat energy. When current flows through a resistor, electrical energy is dissipated as heat.
Q38. In a parallel circuit, current through each resistor depends on
In a parallel circuit, the current through each resistor depends on the resistance of that branch. According to Ohm’s law, I = V/R, and since V is the same across all branches, current is inversely proportional to resistance.
Q39. Electric fan mainly uses electrical energy to produce
An electric fan mainly uses electrical energy to produce mechanical work (rotation of the blades). It also produces some heat, but the main purpose is to create air movement.
Q40. Heating effect of electric current is due to
The heating effect of electric current is due to electrical energy converting to heat energy in the resistor. This happens when electrons collide with atoms in the conductor, transferring energy in the form of heat.
Q41. Fairy lights are difficult to repair because they are connected in
Fairy lights (string lights) are usually connected in series. If one bulb burns out or breaks, the entire string stops working, making it difficult to find the faulty bulb. This is a typical example of a series circuit.
Q42. Heating effect increases when current
According to Joule’s law, H = I²Rt, heat produced is proportional to the square of the current. So when current increases, the heating effect increases dramatically (doubling current quadruples heat).
Q43. Two resistors of 10Ω and 40Ω in parallel have equivalent resistance
For parallel combination: 1/Rp = 1/10 + 1/40 = 4/40 + 1/40 = 5/40 = 1/8. So Rp = 8Ω. The equivalent resistance is 8Ω, which is less than the smallest resistor (10Ω).
Q44. Total resistance of two parallel groups of 8Ω and 10Ω connected in series is
For each parallel group, first find equivalent resistance. For 8Ω group: Rp = 8Ω (assuming single resistor). For 10Ω group: Rp = 10Ω. Then in series: Rs = 8Ω + 10Ω = 18Ω. Total resistance is 18Ω.
Q45. Total current in the above parallel circuit is
Total current cannot be determined without voltage. Assuming 24V: For 8Ω branch, I1 = 24/8 = 3A. For 10Ω branch, I2 = 24/10 = 2.4A. Total I = 3 + 2.4 = 5.4A. With 12V: I1 = 12/8 = 1.5A, I2 = 12/10 = 1.2A, total = 2.7A. The answer depends on voltage.
Q46. The source keeps supplying energy to maintain current because
The source keeps supplying energy to maintain current because energy is continuously dissipated in the resistors as heat (Joule heating). The source must supply this energy to maintain the flow of current.
Q47. Equivalent resistance of 5Ω, 10Ω and 30Ω in parallel is
1/Rp = 1/5 + 1/10 + 1/30 = 6/30 + 3/30 + 1/30 = 10/30 = 1/3. So Rp = 3Ω. The equivalent resistance is 3Ω.
Q48. Energy supplied by a source in time t is
Energy supplied by a source is E = VIt (since V = W/Q and Q = It, so W = VIt). This is the electrical energy consumed in a circuit in time t.
Q49. High resistance in heating elements is required to
High resistance in heating elements is required to produce more heat. According to Joule’s law, H = I²Rt. For a given voltage, higher resistance produces more heat (since H = V²t/R).
Q50. Three resistors of 5Ω, 10Ω, and 30Ω are connected in parallel to 12V. Current through 5Ω is
Using Ohm’s law, I = V/R = 12V / 5Ω = 2.4A. The current through the 5Ω resistor is 2.4 amperes. In a parallel circuit, the current through each resistor is determined by its own resistance.