PRELIMINARY STAGE 2024
Contest 34
T.I. AMASS, Kumasi: 71 points (Winner)
Amenfiman SHS –40 pts
Tuobodom SHTS: 21 points
Contest 35
Accra Girls’ SHS: 39 points (Winner)
Notre Dame Girls’ SHS: 34 points
Aburi Girls’ SHS –27 pts
Contest 36
Anlo SHS: 69 points (Winner)
Tamale Islamic Science SHS –34 pts
Yendi SHS –28 pts
ROUND 4 - TRUE OR FALSE
FIRST SET OF QUESTIONS
PREAMBLE
A battery is connected across a series combination of two resistors of resistances, two ohms and four ohms.
1. The current through the 4-ohm resistor equals twice the current through the 2-ohm resistor.
ANSWER: FALSE
EXPLANATION:
In a series circuit, there is only a single path for the electric charge to flow.
Therefore, the current must be identical at all points in the loop, meaning the current through the 4-ohm resistor equals the current through the 2-ohm resistor.
2. The current supplied by the battery equals the sum of the currents in the two resistors.
ANSWER: FALSE
EXPLANATION:
This statement incorrectly applies Kirchhoff's Current Law for parallel circuits to a series circuit.
In series, the total current supplied by the source does not split or add up; it flows sequentially through every component ($I_{\text{total}} = I_1 = I_2$).
3. The current through the 2-ohm resistor equals twice the current through the 4-ohm resistor.
ANSWER: FALSE
EXPLANATION:
Because the components are connected back-to-back in a single series loop, the current through both resistors is exactly the same, making it impossible for one to be a multiple of the other.
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PRACTICE QUESTIONS
PREAMBLE 1
A 6.0 V battery is connected across a 1.0 Ω and a 2.0 Ω resistor in series.
1. The current is 2.0 A.
ANSWER: TRUE
EXPLANATION:
$I = \dfrac{6.0}{3.0}$.
2. The p.d. across the 2.0 Ω resistor is 4.0 V.
ANSWER: TRUE
EXPLANATION:
$V = IR = 2.0 \times 2.0$.
3. The current in the 1.0 Ω resistor is twice that in the 2.0 Ω resistor.
ANSWER: FALSE
EXPLANATION:
The current is the same in series.
PREAMBLE 2
A 3.0 Ω and a 6.0 Ω resistor are connected in parallel across a battery.
1. The p.d. across each resistor is the same.
ANSWER: TRUE
EXPLANATION:
Both are across the same two points.
2. The current in the 3.0 Ω resistor is twice that in the 6.0 Ω resistor.
ANSWER: TRUE
EXPLANATION:
$I = \dfrac{V}{R}$ with the same V.
3. Their combined resistance is 9.0 Ω.
ANSWER: FALSE
EXPLANATION:
It is $\dfrac{3.0 \times 6.0}{9.0} = 2.0\ \Omega$.
PREAMBLE 3
A lamp and a resistor are in series with a battery, and the resistor is then short-circuited by a wire.
1. The current in the circuit increases.
ANSWER: TRUE
EXPLANATION:
The total resistance falls.
2. The lamp becomes dimmer.
ANSWER: FALSE
EXPLANATION:
It gets the full voltage and becomes brighter.
3. The total resistance of the circuit falls.
ANSWER: TRUE
EXPLANATION:
Only the lamp's resistance remains.