A 12-V battery is connected to a device and 24 mA (24 x 10' Amps) of current flows
through it. If the device obeys Ohm's law, how much current will flow when a 24-V battery
is used?

Correct  Ic₂ = 48 mA = 48 · 10⁻³ A

Explanation:

Given:

U₁ = 12 V  DC  first battery voltage

Ic₁ = 24 mA = 24 · 10⁻³ A   Intensity of current with the first battery

U₂ = 24 V DC    second battery voltage

Ic₂ = ?   Intensity of current with the second battery

The formula that applies to a simple electric circuit under the Ohm's law is:

R = U / Ic  

where R is the total resistance in the electrical circuit and it is constant.

R = U₁ / Ic₁ = U₂ / Ic₂ ⇒ U₁ / Ic₁ = U₂ / Ic₂  ⇒ Ic₂ = (U₂ · Ic₁) / U₁

Ic₂ = (24 · 24) / 12 = 48 mA

Ic₂ = 48 mA = 48 · 10⁻³ A

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