Nomor 17.

Diketahui:

Vp = 220 V

Vs = 55 V

Ip = 0,5 A

Is = 1,5 A

Ditanya:

η = ....?

Jawab:

η = (Vs × Is / Vp × Ip) × 100%

η = (55 × 1,5 / 220 × 0,5) × 100%

η = (82,5 / 110) × 100%

η = 0,75 × 100%

η = 75%

Nomor 18.

Diketahui:

R = 12 ohm

t = 4 menit = 240 detik (s)

I = 4 ampere

Ditanya:

W = ....?

Jawab:

W = I² × R × t

W = 4² × 12 × 240

W = 16 × 12 × 240

W = 46.080 Joule

Nomor 19.

Diketahui:

V = 200 V

I = 8 ampere

t = 20 menit = 1.200 detik (s)

Ditanya:

W = ....?

Jawab:

W = V × I × t

W = 200 × 8 × 1.200

W = 1.920.000 Joule atau 1.920 kilo Joule

Nomor 20.

Diketahui

R = 20 ohm

V = 60 volt

t = 5 menit = 300 s

Ditanya:

W = ....?

Jawab:

W = V² / R × t

W = 20 / 60 × 300

W = 100 Joule

Nomor 21.

Diketahui:

P = 80 W

R = 5 ohm

Ditanya:

I = ....?

Jawab:

P = I² × R

80 = I² × 5

I² = 80/5

I² = √16

I = 4 ampere