Current Electricity
Current Electricity
- In a metre bridge, a 2 Ω resistance is in the left gap and an unknown resistance \(X\) in the right gap. The null point is at 40 cm from the left end. Then \(X\) is Answer: D. 3 Ω 2/X=40/60⇒ X=3\ Ω . 1
- A potentiometer wire 4 m long of resistance 8 Ω is connected in series with a 12 Ω resistor and a 2 V cell of negligible internal resistance. The balancing length for a cell of emf 0.5 V is Answer: C. 2.5 m I=2/20=0.1 A; potential gradient =0.1×8/4=0.2 V/m; l=0.5/0.2=2.5 m. 1
- A galvanometer of resistance 50 Ω gives full-scale deflection for 5 mA. The shunt needed to convert it into an ammeter of range 0–5 A is approximately Answer: D. 0.05 Ω S=I_gG/I-I_g=0.005×50/4.995≈0.05\ Ω . 1
- Kirchhoff’s first law, i.e., ΣI = 0 at a junction, deals with the conservation of (A) charge Kirchhoff’s first law, i.e., ΣI = 0 at a junction, deals with the conservation of charge 1
- When the balance point is obtained in the potentiometer, a current is drawn from Answer: (C) auxiliary battery only In a potentiometer, the auxiliary battery (driver cell) is connected across the potentiometer wire and ke... 1
- Define Potential Gradient. Potential gradient is defined as the potential difference (the fall of potential from the high potential end) per unit length of the wire. 1
- Why should not the jockey be slided along the potentiometer wire? Sliding the jockey on the potentiometer wire decreases the cross sectional area of the wire and thereby affects the fall of potential along... 1
- Are Kirchhoff’s laws applicable for both AC and DC currents? Kirchhoff’s laws are applicable to both AC and DC ’ circuits (networks). For AC circuits with different loads, (e.g. a combination of a resi... 1
- On what factors does the potential gradient of the wire depend? The potential gradient depends upon the potential difference between the ends of the wire and the length of the wire. 1
- Why is potentiometer preferred over a voltmeter for measuring emf? A voltmeter should ideally have an infinite resistance so that it does not draw any current from the circuit. However a voltmeter cannot be... 1
- State the uses of a potentiometer. The applications (uses) of the potentiometer : Voltage divider : The potentiometer can be used as a voltage divider to change the output vol... 1
- What are the disadvantages of a potentiometer? Disadvantages of a potentiometer over a voltmeter : The use of a potentiometer is an indirect measurement method while a voltmeter is a dire... 1
- Distinguish between a potentiometer and a voltmeter. PotentiometerVoltmeter 1. A potentiometer is used to determine the emf of a cell, potential difference and internal resistance.1. A voltmete... 1
- On what factors does the internal resistance of a cell depend? The internal resistance of a cell depends on : Nature of the electrolyte : The greater the conductivity of the electrolyte, the lower is the... 1
- A voltmeter has a resistance 30 Ω. What will be its reading, when it is connected across a cell of emf Data: E = 2V, r = 10 Ω, R = 30 Ω The voltmeter reading, V = IR = ( E/R+r ) R = ( 2/30+10 ) 30 = ( 2/40 ) 30 = 1.5 V 1
- When two cells of emfs. E1 and E2 are connected in series so as to assist each other, their balancing length Data : l₁ = 2.7m (cells assisting), l₂ = 0.3 m (cells opposing) E₁ + E₂ = Kl₁ and E₁ – E₂ = Kl₂ ∴ fracE₁+E₂E₁-E₂=fracK l₁K l₂ ∴ fracE₁E₂=fra... 1
- The emf of a cell is balanced by a length of 120 cm of potentiometer wire. When the cell is shunted by a resistance Data :R = 10 Ω, l₁ = 120 cm, l₂ = 120 – 20 = 100 cm r = R( fracl₁-l₂l₂ ) = 10 ( 120-100/100 ) = 2 Ω The internal resistance of the cell is 2... 1
- A potential drop per unit length along a wire is 5 × 10-3 V/m. If the emf of a cell balances against Data: K = 5 × 10⁻³ V/m , L = 216 cm = 216 × 10⁻² m E = KL ∴ E = 5 × 10⁻³ × 216 × 10⁻² = 1080 × 10⁻⁵ = 0.01080V The emf of the cell is 0.0108... 1
- The resistance of a potentiometer wire is 8 Ω and its length is 8 m. A resistance box and a 2 V Data: R = 8 Ω, L = 8 m, E = 2 V, K = 1 µV/mm = 1 × frac10⁻⁶ ~V10⁻³ ~m = 10⁻³ V/m K = V/L=fracE R(R+R_B) L^(prime) where R_B is the resistanc... 1
- Find the equivalent resistance between the terminals F and B in the network shown in the figure below given Applying Kirchhoff’s voltage law to loop FGHF, we get, – 10I1 – 10(I1 – I2) + 10(I – I1) + 10(I – I1) = 0 ∴ – 10I1 – 10I1 + 10I2 + 10I – 10I... 1
- A voltmeter has a resistance of 100 Ω. What will be its reading when it is connected across a cell of emf 2 V Data: E = 2V, r = 20 Ω, R = 100 Ω The voltmeter reading, V = IR V = ( 2/100+20 )100 = 200/120=10/6 = 1.667 V. 1