Currents

11/17/08

Fig P27-8, p.852

Fig 27-5, p.836

Fig 27-9b, p.841

Hig

h P

oten

tial

Low

Pot

entia

l

dx

dVA

dt

dq

Table 27-1, p.837

Fig 27-3, p.834

Fig 27-9b, p.841

Fig 27-13, p.845

Fig 27-13, p.847

The same potential difference is applied to the two light bulbs shown in the figure. Which one of the following statements is true?

a. The 30 W bulb carries the greater current and has the higher resistance.

b. The 30 W bulb carries the greater current, but the 60 W bulb has the higher resistance.

c. The 30 W bulb has the higher resistance, but the 60 W bulb carries the greater current.

d. The 60 W bulb carries the greater current and has the higher resistance.

Fig 27-13, p.847

The same potential difference is applied to the two light bulbs shown in the figure. Which one of the following statements is true?

c. The 30 W bulb has the higher resistance, but the 60 W bulb carries the greater current.

This is true because the potential difference is the same across the two bulbs so the 60 W bulb must have the higher current because P = VI and the 30 W bulb must have the higher resistance because V = IR.

Fig 27-15, p.847

For the two lightbulbs shown in the figure rank the current values at points a through f from the greatest to the lowest.

Fig 27-15, p.847

For the two lightbulbs shown in the figure rank the current values at points a through f from the greatest to the lowest.

Ia = Ib Ic = Id Ie = If

Ia > Ic > Ie

Problems

1. Suppose that you have 2.10 108 doubly charged positive ions per cubic centimeter all moving in the same direction with a speed 1.4 105 m/s, Can the total current be calculated?

Problems

5. It takes about 50 mV of current to electrocute a person if the current passes near the heart. If an electrician’s resistance is 1800 , what would be a fatal voltage?