Heat and Thermodynamics / ऊष्मा एवं ऊष्मागतिकी
The source introduces heat, temperature, thermal expansion, specific heat and latent heat together with practical applications frequently asked in competitive examinations.
Source Heat, Temperature, Thermal Expansion, Specific Heat तथा Latent Heat को important practical applications के साथ explain करता है।
Heat / ऊष्मा
The source describes heat as a form of energy associated with the sensation or perception of warmness or coldness.
Source Heat को energy का एक form बताता है जो warmness तथा coldness की sensation से associated है।
Units / इकाइयाँ
Calorie, kilocalorie and joule.
1 calorie = 4.18 joules
Temperature / तापमान
Temperature is the measurement of the hotness or coldness of a body.
Body की hotness या coldness के measurement को Temperature कहते हैं।
When two bodies at different temperatures are placed in contact, heat flows from the higher-temperature body to the lower-temperature body.
Different temperatures वाली bodies contact में आने पर heat higher temperature से lower temperature की ओर flow करती है।
Thermometer / थर्मामीटर
A thermometer is used to measure temperature.
Temperature measure करने के लिए Thermometer का use होता है।
Important Temperature Facts / महत्वपूर्ण तथ्य
- Normal human-body temperature in source → 37°C or 98.4°F
- Celsius and Fahrenheit have the same reading at −40°.
- Clinical thermometer range in source → 96°F to 110°F
Absorption and Reflection of Heat / ऊष्मा का अवशोषण एवं परावर्तन
A white roof keeps a house cooler because it reflects more heat radiation and absorbs less, whereas a black surface absorbs more.
White roof अधिक heat rays reflect और कम absorb करती है, जबकि black surface अधिक heat absorb करती है।
Why Does Ice Wrapped in a Blanket Melt Slowly? / कंबल में लिपटी बर्फ धीरे क्यों पिघलती है?
The source explains that a woollen blanket is a poor conductor of heat, so it reduces heat transfer to the ice.
Woollen blanket heat का poor conductor है, इसलिए बाहर की heat ice तक जल्दी नहीं पहुँचती।
Conductor of Heat / ऊष्मा चालक
The source identifies silver as the best conductor of heat.
Source Silver को best conductor of heat बताता है।
Thermal Expansion / तापीय प्रसार
Thermal expansion is the increase in size of a body on heating.
Heating के कारण body के size में increase को Thermal Expansion कहते हैं।
Types of Expansion in Solids / ठोस में प्रसार के प्रकार
- Linear Expansion / रेखीय प्रसार
- Superficial Expansion / क्षेत्रीय प्रसार
- Cubical Expansion / आयतन प्रसार
Applications / अनुप्रयोग
- Telephone wires are kept loose to allow contraction in winter.
- Gaps are provided between railway tracks to allow expansion in summer.
Specific Heat / विशिष्ट ऊष्मा
The amount of heat required to raise the temperature of unit mass of a substance by 1°C is called its specific heat.
Unit mass substance का temperature 1°C बढ़ाने के लिए required heat को Specific Heat कहते हैं।
Anomalous Expansion of Water / जल का असामान्य प्रसार
The source states that as water is heated from 0°C to 4°C its volume decreases and becomes minimum at 4°C; above 4°C its volume increases.
0°C से 4°C तक water को heat करने पर उसका volume decrease होता है और 4°C पर minimum होता है। इसके बाद volume increase होता है। इसे Anomalous Expansion of Water कहा जाता है।
Latent Heat / गुप्त ऊष्मा
Heat absorbed or released per unit mass during a change of state at constant temperature is called latent heat.
Constant temperature पर state change के दौरान per unit mass absorbed या released heat को Latent Heat कहते हैं।
- Latent heat of fusion of ice → 80 cal/g
- Latent heat of vaporisation of steam → 536 cal/g
Steam Burns / भाप से जलना
The source states that steam burns are more severe than hot-water burns because steam possesses high latent heat.
Quick Revision / त्वरित पुनरावृत्ति
- 1 calorie → 4.18 joules
- Normal body temperature → 37°C in source
- Celsius = Fahrenheit → −40°
- Best heat conductor in source → Silver
- Railway gaps → Thermal expansion
- Water minimum volume → 4°C
- Latent heat of fusion of ice → 80 cal/g
- Latent heat of vaporisation of steam → 536 cal/g