Here are the solutions to questions 10, 11, 12, and 13.
10. A glass flask of volume 100cm3 is filled to the brim with liquid whose cubical coefficient of expansion is 1×10−3per∘C. The flask and its liquid content are originally at 20∘C. Determine the volume of liquid which will overflow upon heating the flask to 50∘C if the coefficient of linear expansion of glass is 8×10−6per∘C.
Step 1: Identify the given values and calculate the change in temperature.
Initial volume, V0=100cm3.
Cubical coefficient of expansion of liquid, γliquid=1×10−3per∘C.
Linear coefficient of expansion of glass, αglass=8×10−6per∘C.
Initial temperature, T1=20∘C.
Final temperature, T2=50∘C.
Change in temperature, ΔT=T2−T1=50\circC−20\circC=30∘C.
Step 2: Calculate the cubical coefficient of expansion for glass.
The cubical coefficient of expansion for a solid is approximately three times its linear coefficient of expansion:
γglass=3αglass=3×(8×10−6per\circC)=24×10−6per\circC
Step 3: Calculate the change in volume for the liquid and the flask.
The change in volume is given by ΔV=V0γΔT.
For the liquid:
ΔVliquid=V0γliquidΔT=(100cm3)×(1×10−3per\circC)×(30\circC)
ΔVliquid=3cm3
For the flask:
ΔVflask=V0γglassΔT=(100cm3)×(24×10−6per\circC)×(30\circC)
ΔVflask=0.072cm3
Step 4: Determine the volume of liquid that overflows.
The volume of liquid that overflows is the difference between the expansion of the liquid and the expansion of the flask.
ΔVoverflow=ΔVliquid−ΔVflask
ΔVoverflow=3cm3−0.072cm3
ΔVoverflow=2.928cm3
The volume of liquid that will overflow is 2.928cm3.
11. 500cm3 of water is to be heated from room temperature (28∘C) to 100∘C in order to prepare hot cup of coffee. (a) What is the minimum heat required? (b) How long will it take to heat the water with a 1000W heating coil which has a heating efficiency of 70%?
Given constants:
- Density of water, ρwater=1g/cm3=1000kg/m3.
- Specific heat capacity of water, cwater=4186J/kg∘C.
a) What is the minimum heat required?
Step 1: Calculate the mass of the water.
Volume of water, V=500cm3.
m=ρV=(1g/cm3)×(500cm3)=500g=0.5kg
Step 2: Calculate the change in temperature.
Initial temperature, T1=28∘C.
Final temperature, T2=100∘C.
ΔT=T2−T1=100\circC−28\circC=72\circC
Step 3: Calculate the minimum heat required using Q=mcΔT.
Q=(0.5kg)×(4186J/kg\circC)×(72\circC)
Q=150696J
The minimum heat required is 150696J.
b) How long will it take to heat the water with a 1000W heating coil which has a heating efficiency of 70%?
Step 1: Calculate the useful power of the heating coil.
Power of heating coil, P=1000 W.
Efficiency, η=70%=0.70.
Puseful=ηP=0.70×1000W=700W
Step 2: Calculate the time taken using Q=Pusefult.
t=PusefulQ=700W150696J
t≈215.28s
To convert to minutes:
t=60215.28min≈3.59min
It will take approximately 215.28s (or 3.59 min).
12. A 40kg metal slab at temperature 600∘C is taken from a furnace and plunged into 300kg of oil originally at 25∘C. The final temperature of the oil/slab is 40∘C. Determine the specific heat capacity of the metal if that of oil is 2100J/kg.∘C.
Step 1: Identify the given values.
Mass of metal, mmetal=40 kg.
Initial temperature of metal, Tmetal,1=600∘C.
Mass of oil, moil=300 kg.
Initial temperature of oil, Toil,1=25∘C.
Final equilibrium temperature, Tf=40∘C.
Specific heat capacity of oil, coil=2100J/kg∘C.
Step 2: Apply the principle of calorimetry (Heat lost by metal = Heat gained by oil).
mmetalcmetal(Tmetal,1−Tf)=moilcoil(Tf−Toil,1)
Step 3: Substitute the values into the equation.
(40kg)×cmetal×(600\circC−40\circC)=(300kg)×(2100J/kg\circC)×(40\circC−25\circC)
40×cmetal×560=300×2100×15
22400×cmetal=9450000
Step 4: Solve for cmetal.
cmetal=224009450000
cmetal=421.875J/kg\circC
The specific heat capacity of the metal is 421.875J/kg\circC.
13. A 100g ice-block at −20∘C is dumped into a thermally insulated container of water at 0∘C. How much water is frozen if the specific heat of ice is 2302J/Kg.∘C and latent heat of fusion is 3.35×105 J/Kg?
Step 1: Identify the given values.
Mass of ice, mice=100g=0.1 kg.
Initial temperature of ice, Tice,1=−20∘C.
Initial temperature of water, Twater,1=0∘C.
Specific heat capacity of ice, cice=2302J/kg∘C.
Latent heat of fusion of ice, Lf=3.35×105 J/kg.
The problem implies that the final equilibrium temperature is 0∘C, and some water freezes. This means the heat gained by the ice to warm up to 0∘C is supplied by the freezing of some of the water.
Step 2: Calculate the heat gained by the ice to warm from −20∘C to 0∘C.
Qice,warm=micecice(0\circC−Tice,1)
Qice,warm=(0.1kg)×(2302J/kg\circC)×(0\circC−(−20\circC))
Qice,warm=(0.1kg)×(2302J/kg\circC)×(20\circC)
Qice,warm=4604J
Step 3: Determine the mass of water that freezes