Date:-_________________________________
Group:_________________________________
Name:__________________________________
1.
Problem :
A steel rod 2 m long is fastened at one end to a fixed support and is free to expand or contract. If the ambient temperature rises by 25°C, how much will the rod expand or contract? Use the thermal expansion coefficient for steel
 steel
=11.7x10
-6 o C -1 .
Solution:
2. Problem : An insulating material placed inside the walls of a home is 6 in. thick. The heat flow is calculated to be 4.2 Btu/hr when the inside temperature is 70 °F and the outside temperature is 0 °F.
Determine the thermal conductivity of the insulating material as the heat flow passes through 1 ft 2 of the wall. In addition to expressing k in units of Btu/(hr ft o F), convert your units to SI units using watts, meters, and Kelvin temperature. Using Table 2 identify what insulating material was used. Use units conversion Table A-7 attached (page 6 of this document).
Solution:
1

3.
Briefly describe the two mechanisms responsible for the thermal conductivity of materials.
Why thermal conductivity of metals is usually much higher than that of polymers?
4. Problem
( a) A metallic wire 100 cm long has a diameter of 0.05 cm. If it has a resistance of 0.08 Ω when
10A of current are running through the circuit at standard temperature, find the wire's resistivity in Ω ·cm. (b) Using Table 3, identify the material from which the wire was fabricated.
Solution:
5. Problem:
A rectangular block of aluminum has the dimensions 25 mm x 25 mm x 50 mm.
(a) Make a three-dimensional sketch of the block and place dimensions on it.
(b) What is the resistivity of the block, in µΩ·cm, measured between the two squared ends, at 20°C?
(c) Determine the resistance and the electrical conductivity for aluminum at 20°C. (Use Table 3)
Solution:
2

6. Problem
An electric wire carries a 30-A current. It is oriented in a magnetic field whose width is 12 cm at an angle of 40°.
The magnetic field (B) is 0.90 T. Find the force acting on the wire.
Fig 1. (a) Bar magnet (b) Magnetic field lines of a bar magnet. (c) A magnetic field B with a length of wire (I) and crossing it at an angle (9) to the horizontal
Solution:
3

7. Problem
Two sheets of copper with a total area of 1 m
2
separated at a distance of 0.05 mm by paper (dielectric constant = 3.5). Find the capacitance, how does this compare with the capacitance when the sheets are separated by air?
Solution:
Solution:
8.
Problem:
Show by drawing how the relative position of the positive and negative charges varies under the influence of an applied electric field in the case of electronic, ionic and molecular polarization.
4

Free electron rest mass m o
Boltzmann’s constant k
Planck’s constant h
Electronic charge q
Intrinsic carrier concentration of Si n i
Room temperature value of kT
DATA SHEET:
9.11xl0
-31 kg
1.38 x 10 -23 J/ o K = 8.618x10
-5 eV/K
6.63x10
-34 J s
1.6 x 10 -19 C
1.5 x 10 10 cm -3
0.0259 eV
Energy band gap E g of Si
Permittivity of vacuum

0
Reduced Planck’s constant
Speed of light
1.1 eV
8.85 x 10
-14
F/cm
  h / 2

3 x 10
8
m/s
ΔT=1 o C = 1 K = 1.8°F; 1W = 3.41214 BTU/h; 1 ft = 0.3048 m; 1 ft = 12 in
E b
 m n
* q 4
2 K 2  2
;
K

4

0
 r
; f ( E )

1
 exp

( E
1

E
F
) / kT
 f ( E
F
)


1
 exp

( E
F

E
F
) / kT
 

1 
1
1

1

1
2
; n
0


E c
 f ( E ) N ( E ) dE
N c n
0

2 (
2
 m n
* kT h
2
)
3 / 2

N c exp


( E c
;

E
F
) /
N v

2 (
2
 m * p kT h
2
)
3 / 2 kT
 ; p
0

N v exp


( E
F

E v
) / kT
 ; n i

N c
N v e

E g
/ 2 kT n
0 p
0
 n i
2
; n
0
 n i exp

( E
F

E i
) / kT
 ; p
0
 n i exp

( E i

E
F
) / kT
 ;
𝑖
𝑛
C
 k

0
A / d
;
𝑝
;
0
𝐸 𝑔
2𝐾𝑇
;
𝑛
 
1 /
 ;  t

 l l
0
   t
;
R

0
𝑛
;
𝑝
 l
A
;
 t
  t
 l
0
; k
 q
A

 d
 t
;
F

I
 l

B

Sin

0
𝑝
;
; n
 c / v ; v
 l
 f
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