PHY025_Physics 2_C 4 Notes, Tutorials and Practical’s
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Tutorial 1: Current , Charge and Drift velocity
1. Convert these currents into amperes 6. In the circuit on below, the two bulbs are of
a. 500 mA different sizes and brightness.
b. 2500 mA a. What type of meter is meter X?
2. Convert these currents into milliamperes b. What type of meter is meter Y?
a. 2.0 A c. What is the reading on meter Y?
b. 0.1 A d. How much potential energy does each
3. coulomb have as it leaves the battery?
a. Draw the circuit below using circuit symbols. e. How much potential energy is lost by each
coulomb passing through bulb A?
f. How much charge passes through A every
second?
g. How much energy is radiated from A every
second?
b. On your diagram, mark and label the
conventional current direction and the
direction of electron flow.
c. The current reading on one ammeter is shown.
7. Calculate
What is the reading on the other one?
a. The charge passed through a torch bulb in 5
d. Which bulb(s) will go out if the switch contacts
minutes when the torch bulb carries a steady
are moved apart? Give a reason for your
current of 0.3A,
answer.
8. The number of electrons hitting the screen of a
4. What charge is delivered if
TV tube each second when the beam current is
a. a current of 10 A flows for 5 seconds
1 mA. Assume the charge of an electron = -1.6 x
b. a current of 250 mA flows for 40 seconds?
10-19 C.
9. Estimate the drift velocity of free electrons
along a copper wire of diameter 0.4 mm
carrying a steady current of 5.0 A. Assume that
5. In what unit is each of these measured?
copper contains 1.6 x 10-22 electrons per m3.
a. PD
10. In an electrolysis experiment, a steady current
b. EMF
of 0.40 A is passes for 20 minutes through a cell
c. Charge
containing copper sulphate solution. Both
d. Energy
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PHY025_Physics 2_C 4 Notes, Tutorials and Practical’s
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electrodes in the cell are copper plates. Copper 13. A semiconducting strip 6.0 mm and 0.50 mm
ions from the solution are attracted to the thick carries a current of 10mA, as shown in
cathode and neutralized by gaining two Figure.
electrons per ion. Each copper atom leaving the
anode goes into solution as a copper ion by
releasing two electrons, Calculate the
a. The total charge passed
b. The number of copper atoms deposited on the e. If the value of n for the semiconducting
cathode material is 7.0 × 1022 𝑚−3 , show that the drift
c. The mass deposited on the cathode, given each speed of the charge carriers, which carry a
copper atom has a mass of 1.1 x 10-25 kg. charge of 1.6 x 10-19 C, is about 0.3 𝑚𝑠 −1 .
11. The beam current in a television tube is 32 mA. f. The drift speed for electrons in a copper strip
The electrons travel at a speed of 4.2 × 10 𝑚𝑠 7 −1
of the same dimensions and carrying the
through a distance of 21 cm. same current would be about 10−7 𝑚𝑠 −1 . Use
the equation to explain why this value is very
different from that of the semiconductor.
14. The current in the tungsten filament of a torch
bulb is 25 mA.
g. How much charge will conduct through the
filament in 8.0 minutes.
h. How many electrons will flow through the
a. Show that the number of electrons striking filament during this time?
the screen in 1 hour is 7.2 × 1020 i. The bulb is connected to the cell in
b. Calculate the number of electrons in the beam the torch by two copper leads. Discuss the
at any instant. [Ans 1.2 × 109 ] factors that would cause a difference between
12. A typical flash of lightning lasts for about 0.5ms, the drift speed of the electrons in the copper
during which time it discharges approximately leads and that of the electrons in the filament.
8 C of charge.
c. Calculate the average current in such a strike?
d. The current is caused by positive ions having
a charge 1.6 x 10-19 C travelling from the Earth
to the thundercloud. How many such ions are
there in the strike?
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