EIT Electrical, Thermodynamics & Fluid Systems 3

Question 1

Which law states that the algebraic sum of currents at any node in a circuit equals zero?

Accepted Answer

Kirchhoff's Current Law

Answer

KCL (Kirchhoff's Current Law) is based on charge conservation: Σ I_in = Σ I_out at any node.

Question 2

The coefficient of performance (COP) of a Carnot refrigerator operating between T_H = 300 K and T_L = 250 K is:

Accepted Answer

5.0

Answer

COP_Carnot,ref = T_L / (T_H − T_L) = 250 / (300 − 250) = 5.0.

Question 3

The hydraulic diameter of a rectangular duct with width 0.4 m and height 0.2 m is:

Accepted Answer

0.267 m

Answer

D_h = 4A/P = 4(0.4×0.2) / [2(0.4+0.2)] = 0.32/1.2 ≈ 0.267 m.

Question 4

An ideal transformer has 200 primary turns and 50 secondary turns. If the primary voltage is 120 V, what is the secondary voltage?

Accepted Answer

30 V

Answer

V_s/V_p = N_s/N_p → V_s = 120 × (50/200) = 30 V.

Question 5

For an ideal gas undergoing an isothermal process, which pair of quantities remains constant?

Accepted Answer

Temperature and internal energy

Answer

For an ideal gas, internal energy depends only on temperature; if T is constant, so is u.

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