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Expert-verifiedWhy should you not connect an ammeter directly across a voltage source as shown in Figure 21.48? (Note that script E in the figure stands for emf.)
One should not connect an ammeter directly across a voltage source because it can cause a short circuit.
When the two terminals of a battery get in direct contact through a wire, when no load is attached to the wire, a large amount of current flows through it. Due to the flow of a large amount of current, the wire burns up, and the circuit breaks. This condition of the circuit is known as a Short circuit.
To measure the current accurately we need an ammeter with the least resistance possible. This means that if we connect an ammeter directly to the circuit, it will offer almost no resistance and will create a condition called short-circuit. This could damage the ammeter.
Therefore, we should not connect an ammeter directly across a voltage source as it causes a short circuit.
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