Solutions to Government Exam Questions

1.         R_T = [R₁^-1 + R₂^-1  + R₃^-1]^-1 = [100^-1 + 100^-1 + 100^-1] ^-1 = 33.3 W.

2.         A_c because it is the total current.

3.         V_T = IR_T

            9 = I ( 2 + 4 + 5+ 7)

            I = 0.5 A

4.         Circuit M         

V_T = IR_T

            12 = I ( 3 + 9 + 12)

            I = 0.5 A

            Circuit N needs 10 times the current, so we need 10 (0.5 A) =  5A

            Resistance? V = IR

                        12 = 5R

                        R = 2.4 W.

            Which two resistors will give 2.4 W?

            Try them into the formula:          R_T = [R₁^-1 + R₂^-1  ]^-1 = [3^-1 + 12^-1 ]^-1 = 2.4 W.

            Answer 3 W And 12 W.

5.         Voltage is constant! Answer 12 V

6.         C

7.         V_T = I R_T = 0.25(10 + 20 + 40) = 17.5 V.

8.         I_T = 0.75 + 0.75 = 1.5 A

9.         If the resistance at the second bulb is twice as big, then it will draw only half the current. 0.5(0.6) = 0.3 A.

            Attach an ammeter to L₂ to check if this is the case.