Final answer:
To find the value of resistance for a potential difference of 2.4 V across each bulb, one would typically use Ohm's law, which relates voltage (V), current (I), and resistance (R). Examples illustrate calculations of resistance given current and voltage. Without specific circuit details, the exact value of resistance for 2.4 V across each bulb cannot be determined.
Step-by-step explanation:
To find the value of r for which the potential difference across each of the bulbs would be 2.4 V, one would follow a similar approach as in the provided examples, using Ohm's law.
In the example where the current is 1.25 A and the voltage supply is 4 V for a bulb, the resistance (R) is calculated using the equation R = V/I. Applying this gives us a resistance of 4 V / 1.25 A = 3.2 Ω. If the voltage supply is increased to 7 V, the current in the bulb would subsequently increase, assuming the resistance remains constant, and it is calculated again using Ohm's law, I = V/R, giving a current of 7 V / 3.2 Ω = 2.1875 A.
When analyzing circuits, the power (P), voltage (V), resistance (R), and current (I) are related by formulas such as P = V^2/R and P = I^2R. For example, a headlight drawing 2.50 A under a 12.0 V applied voltage would have a resistance of 12.0 V / 2.50 A = 4.8 Ω. In a circuit where multiple components like bulbs are used, each component will have its potential difference and current determined by Ohm's law if their resistance is known.
Therefore, to find the resistance for a given potential difference of 2.4 V across each bulb, you must know the configuration of the circuit (whether it's series or parallel) and the total voltage or current if other components are involved. If no other information is given, we lack the context necessary to provide an exact value for r.