1. The SI unit of surface energy is dimensionally equivalent to which of the following?
A.
N m
B.
N m^-1
C.
N m^-2
D.
kg m s^-2
Correct Answer:
N m^-1
Explanation:
Surface energy is energy per unit area. Since energy has unit J = N m, its SI unit is J m^-2 = N m^-1.
2. Which expression represents the SI base-unit form of surface energy?
A.
kg s^-2
B.
kg m s^-2
C.
kg m^-1 s^-2
D.
kg m^2 s^-2
Correct Answer:
kg s^-2
Explanation:
The SI unit of surface energy is J m^-2. Using J = kg m^2 s^-2, J m^-2 becomes kg s^-2.
3. A surface energy density is measured as 0.36 J m^-2. Which equivalent SI unit notation is correct?
A.
0.36 N m
B.
0.36 N m^-1
C.
0.36 N m^-2
D.
0.36 kg m s^-1
Correct Answer:
0.36 N m^-1
Explanation:
Because 1 J m^-2 = (1 N m)m^-2 = 1 N m^-1, 0.36 J m^-2 equals 0.36 N m^-1.
4. Which of the following quantities has the same SI unit as surface energy?
A.
Force
B.
Pressure
C.
Surface tension
D.
Energy
Correct Answer:
Surface tension
Explanation:
Surface energy is energy per unit area and has unit J m^-2, which is equivalent to N m^-1, the SI unit of surface tension.
5. The unit kg s^-2 is written in a derived SI form as which unit of surface energy?
A.
J m^-2
B.
J m^-1
C.
N m
D.
N m^-2
Correct Answer:
J m^-2
Explanation:
Since 1 J = 1 kg m^2 s^-2, dividing by m^2 gives 1 J m^-2 = 1 kg s^-2.
6. A material has surface energy 250 mJ m^-2. Express this value in the equivalent SI unit N m^-1.
A.
0.025 N m^-1
B.
0.25 N m^-1
C.
2.5 N m^-1
D.
250 N m^-1
Correct Answer:
0.25 N m^-1
Explanation:
Since 1 J m^-2 = 1 N m^-1, 250 mJ m^-2 = 250 × 10^-3 N m^-1 = 0.25 N m^-1.
7. Which dimensional formula corresponds to the SI unit of surface energy?
A.
[M L^2 T^-2]
B.
[M L T^-2]
C.
[M T^-2]
D.
[M L^-1 T^-2]
Correct Answer:
[M T^-2]
Explanation:
Surface energy has unit J m^-2. The dimensional formula of joule is [M L^2 T^-2]; division by L^2 gives [M T^-2].
8. An energy of 4.8 × 10^-3 J is associated with an area of 2.0 × 10^-2 m^2. What is the surface energy in SI units?
A.
2.4 × 10^-1 J m^-2
B.
2.4 × 10^-2 J m^-2
C.
9.6 × 10^-5 J m^-2
D.
9.6 × 10^-1 J m^-2
Correct Answer:
2.4 × 10^-1 J m^-2
Explanation:
Surface energy equals energy divided by area: (4.8 × 10^-3)/(2.0 × 10^-2) = 2.4 × 10^-1 J m^-2.
9. Which conversion of surface energy units is correct?
A.
1 erg cm^-2 = 10^-1 J m^-2
B.
1 erg cm^-2 = 10^-2 J m^-2
C.
1 erg cm^-2 = 10^-3 J m^-2
D.
1 erg cm^-2 = 10^-4 J m^-2
Correct Answer:
1 erg cm^-2 = 10^-3 J m^-2
Explanation:
One erg is 10^-7 J and one cm^2 is 10^-4 m^2. Therefore, 1 erg cm^-2 = 10^-7/10^-4 J m^-2 = 10^-3 J m^-2.
10. A surface energy is reported as 7.5 × 10^2 dyn cm^-1 in the CGS system. What is its value in the SI unit J m^-2?
A.
7.5 × 10^-2 J m^-2
B.
7.5 × 10^-1 J m^-2
C.
7.5 J m^-2
D.
75 J m^-2
Correct Answer:
7.5 × 10^-1 J m^-2
Explanation:
Since 1 dyn cm^-1 = 10^-3 N m^-1 = 10^-3 J m^-2, 7.5 × 10^2 dyn cm^-1 equals 7.5 × 10^-1 J m^-2.
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