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🔢 Sources of Energy – Numericals

Class 10 Science • Chapter 14 • Easy to Expert

📘 Numerical Practice

इस chapter में numerical questions मुख्यतः energy, power, efficiency और energy conversion से जुड़े होते हैं। पहले खुद solve करें और उसके बाद solution check करें।

Energy E = Pt
Power P = E/t
Efficiency η = Useful Output/Input × 100
1 kWh = 3.6 × 10⁶ J
🎯 Difficulty
20 TOTAL
4 EASY
8 HARD + VERY HARD
4 EXPERT
Numerical 1 – Energy
EASY
Energy
A machine has a power of 500 W and works for 20 seconds. How much energy does it convert?
Power को time से multiply करेंगे। Time seconds में है, इसलिए answer joule में मिलेगा।
✅ Solution
P = 500 W
t = 20 s
E = Pt
E = 500 × 20 = 10000 J
Answer: 10,000 J
Numerical 2 – Power
EASY
Power
An appliance converts 2400 J of energy in 20 seconds. Calculate its power.
Power = energy ÷ time.
✅ Solution
P = E/t
P = 2400/20
Answer: 120 W
Numerical 3 – Efficiency
EASY
Efficiency
A device receives 1000 J of energy and gives 800 J of useful output. Find its efficiency.
Useful output को input से divide करके 100 से multiply करें।
✅ Solution
η = Useful Output/Input × 100
η = 800/1000 × 100
Answer: 80%
Numerical 4 – kWh Conversion
EASY
Energy Unit
Convert 2 kWh of electrical energy into joules.
1 kWh = 3.6 × 10⁶ J. इसलिए 2 से multiply करें।
✅ Solution
1 kWh = 3.6 × 10⁶ J
2 kWh = 2 × 3.6 × 10⁶
Answer: 7.2 × 10⁶ J
Numerical 5 – Daily Energy
MODERATE
Solar Energy
A solar-powered device has a power rating of 200 W. If it operates for 5 hours, calculate the energy produced or used in kWh.
200 W को 0.2 kW में बदलें। फिर power × time करें।
✅ Solution
P = 200 W = 0.2 kW
E = Pt
E = 0.2 × 5
Answer: 1 kWh
Numerical 6 – Output Energy
MODERATE
Efficiency
A power system receives 5000 J of energy and operates with 70% efficiency. Find the useful output energy.
Efficiency 70% का मतलब input energy का 70% useful output है।
✅ Solution
Useful output = 70/100 × 5000
Answer: 3500 J
Numerical 7 – Power Conversion
MODERATE
Power
A generator produces 18,000 J of electrical energy in 60 seconds. Find its average output power.
Power = Energy ÷ Time.
✅ Solution
P = E/t
P = 18000/60
Answer: 300 W
Numerical 8 – Efficiency Percentage
MODERATE
Efficiency
A solar device receives 4000 J of solar energy and produces 2400 J of useful energy. Find its efficiency.
Useful output / input × 100.
✅ Solution
η = 2400/4000 × 100
Answer: 60%
Numerical 9 – Five Hour Generation
HARD
Power + Energy
A wind turbine supplies an average electrical power of 2 kW for 5 hours. Calculate the electrical energy generated.
Power kW में और time hour में है, इसलिए answer सीधे kWh में मिलेगा।
✅ Solution
E = Pt
E = 2 × 5
Answer: 10 kWh
Numerical 10 – Energy in Joules
HARD
Energy Conversion
A hydroelectric generator delivers 500 kW of output power for 30 minutes. Calculate the output energy in joules.
500 kW को 500,000 W और 30 minutes को 1800 seconds में बदलें।
✅ Solution
P = 500 kW = 500000 W
t = 30 × 60 = 1800 s
E = Pt
E = 500000 × 1800
Answer: 9 × 10⁸ J
Numerical 11 – Useful Output
HARD
Efficiency
A power plant receives 10,000 kJ of input energy and has an efficiency of 35%. Calculate its useful output energy.
Output = efficiency × input. 35% को 0.35 लिखें।
✅ Solution
Useful output = 0.35 × 10000
Answer: 3500 kJ
Numerical 12 – Required Power
HARD
Power
A system must supply 720,000 J of useful energy in 10 minutes. What average useful power is required?
10 minutes को seconds में convert करें: 600 s. फिर P = E/t।
✅ Solution
t = 10 × 60 = 600 s
P = 720000/600
Answer: 1200 W = 1.2 kW
Numerical 13 – Plant Efficiency
VERY HARD
Efficiency
A plant receives 50 MJ of energy and delivers 15 MJ as useful output. Find its efficiency.
Both input और output same unit में हैं, इसलिए direct output/input × 100 कर सकते हैं।
✅ Solution
η = 15/50 × 100
Answer: 30%
Numerical 14 – Solar Output
VERY HARD
Solar Energy
A solar installation produces 3 kW of useful electrical power for 6 hours each day. Calculate its useful daily energy generation.
kW × hour करने पर energy kWh में मिलेगी।
✅ Solution
E = Pt
E = 3 × 6
Answer: 18 kWh per day
Numerical 15 – Monthly Energy
VERY HARD
Renewable Energy
A small wind installation generates 4 kWh per day. How much energy does it generate in 30 days?
Daily generation को 30 से multiply करें।
✅ Solution
Monthly energy = 4 × 30
Answer: 120 kWh
Numerical 16 – Input Energy from Efficiency
VERY HARD
Efficiency
A machine has an efficiency of 40% and produces 8 MJ of useful output energy. Find the input energy.
Efficiency = output/input. Input = output ÷ efficiency.
✅ Solution
0.40 = 8/Input
Input = 8/0.40
Answer: 20 MJ
Numerical 17 – Energy Conversion
EXPERT
Power + Efficiency
A system receives 5 kW of input power and operates with an efficiency of 60%. Find its useful output power and useful energy generated in 4 hours.
पहले useful power = 60% of 5 kW. फिर useful power × 4 hours से energy निकालें।
✅ Step-by-Step Solution
Useful power = 0.60 × 5 = 3 kW
Useful energy = 3 × 4
Answer: Useful Power = 3 kW; Energy = 12 kWh
Numerical 18 – kWh to Joule
EXPERT
Energy Conversion
A solar system supplies 12.5 kWh of energy. Express this energy in joules.
1 kWh = 3.6 × 10⁶ J. 12.5 से multiply करें।
✅ Solution
E = 12.5 × 3.6 × 10⁶
E = 45 × 10⁶ J
Answer: 4.5 × 10⁷ J
Numerical 19 – Daily to Annual Energy
EXPERT
Energy Generation
A renewable-energy system produces an average of 8 kWh of useful energy every day. Estimate the energy generated in one year using 365 days.
Daily generation को 365 से multiply करें।
✅ Solution
Annual energy = 8 × 365
Answer: 2920 kWh
Numerical 20 – Final Mixed Challenge
EXPERT
Power + Efficiency + Energy
A power system receives 10 kW of input power and has an efficiency of 75%. It operates for 8 hours. Find the useful output power and total useful energy generated in kWh.
पहले input power का 75% निकालकर useful power पाएँ। फिर useful power को 8 hours से multiply करें।
✅ Step-by-Step Solution
Useful power = 75/100 × 10
Useful power = 7.5 kW
Useful energy = 7.5 × 8
Answer: Useful Power = 7.5 kW; Useful Energy = 60 kWh
🔎 इस difficulty में कोई numerical उपलब्ध नहीं है।

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