1). A current of $(25 \\mu A)$ passes through a wire for 4 min . Charge flown through the wire is
1) 6 mC
2) $(6 \\times 10^{-4} C)$
3) $(6 \\mu C)$
4) 60 mC
Hint: q = it = 25 x 10-6 x (4 x 60) = 60 x 10 - 4 = 6 x 10 -3 = 6 mC
2). X bivalent negative ions flow, through an electrolyte to the right, per sec and Y monovalent positive ions flow to the left per sec. The current through the electrolyte is
1) e (2X - Y) to the left
2) e (Y + 2X) to the right
3) e (2Y - X) to the right
4) e (Y + 2X) to the left
Hint: ix = 2eX (to left) iy=eY (to left) i = 2eX + eY = e (2X + Y) (to left)
3). $(10^{16})$ doubly charged positive sodium ions cross any cross-section of an electrolyte per sec, to the left. The current through the electrolyte is
1) 3.2 mA to left.
2) 1.6 mA to right.
3) 3.2 mA to right.
4) 1.6 mA to left.
Hint: $$\\begin{aligned} i &= \\frac{q}{t}=\\frac{N(2 e)}{t} \\\\ i &= 10^{16} \\times 2 \\times 1.6 \\times 10^{-19} \\\\ &= 3.2 \\times 10^{-3} A=3.2 mA \\end{aligned}$$Positive ions move to the right. Therefore, current is directed to the right.
4). In hydrogen atom, the electron makes $(6.6 \\times 10^{15})$ revolutions per second around the nucleus in an orbit of radius $(0.5 \\times 10^{-10} m)$. It is equivalent to a current nearly
1) 1 A
2) 1 mA
3) $(1 \\mu A)$
4) $(1.6 \\times 10^{-19} A)$
Hint: i=qv=1.6 x 10-19 x 6.6 1015 = 10.56 x 10-4 A = 1 mA