A high-resistance voltmeter placed across a battery shows $6.0\ \text{V}$. When the battery is joined in series with a lamp of resistance $10\ \Omega$, the voltmeter reading drops to $5.6\ \text{V}$. Which statement accounts for this observation?
- AThe electromotive force (e.m.f.) of the battery decreases because more work is done across its internal resistance.
- BThe e.m.f. of the battery decreases because work is done across the lamp.
- CThe potential difference (p.d.) across the battery decreases because more work is done across its internal resistance.
- DThe p.d. across the battery decreases because work is done across the lamp.