Internal resistance, emf, cells in series and parallel
- The terminal voltage of the battery, whose emf is 10 V and internal resistance 1 Ω, when connected through an external resistance of 4 Ω as shown in the figure is : Answer: 4. 8 V Key idea: Terminal voltage V=ε-Ir . Current I=ε/R+r=10/4+1=2 A. V=10-2×1=8 V (equivalently IR=2×4=8 V). Option 4. 1
- In a potentiometer circuit a cell of EMF 1.5 V gives balance point at 36 cm length of wire. If another cell of EMF 2.5 V replaces the first cell, then at what length of the wire, the balance point occurs ? Answer: 1. 60 cm Key idea: in a potentiometer, EMF ∝ balancing length. E₂/E₁=l₂/l₁⇒ l₂=36×2.5/1.5=60 cm. Option 1. 1
- A battery consists of a variable number 'n' of identical cells (having internal resistance 'r' each) which are connected in series. The terminals of the battery are short-circuited and the current I is measured. Which of the graphs shows the correct… Answer: 1. (graph: I constant, horizontal line vs n) For n identical cells in series, total emf is nE and total internal resistance is nr .... 1
- A set of 'n' equal resistors, of value 'R' each, are connected in series to a battery of emf 'E' and internal resistance 'R'. The current drawn is I. Now, the 'n' resistors are connected in parallel to the same battery. Then the current drawn from ba… Answer: 1. 10 Series: total resistance nR+R , so I=E/(n+1)R . Parallel: total resistance R/n+R=(n+1)R/n , so I'=nE/(n+1)R . I'/I=n=10⇒ n=10 1
- A potentiometer is an accurate and versatile device to make electrical measurements of E.M.F. because the method involves : Answer: 2. a condition of no current flow through the galvanometer Key idea: at the balance point no current flows through the galvanometer,... 1
- A potentiometer wire is 100 cm long and a constant potential difference is maintained across it. Two cells are connected in series first to support one another and then in opposite direction. The balance points are obtained at 50 cm and 10 cm from th… Answer: 4. 3 : 2 Key idea: balance length is proportional to the emf in the circuit. Supporting: ε₁+ε₂∝50 ; opposing: ε₁-ε₂∝10 . So ε₁∝30 an... 1