251.

Two cells, having the same emf, are connected in series through an external resistance R. Cells have internal resistances r₁ and r₂ (r₁ > r₂) respectively. When the circuit is closed, the potential difference across the first cell is zero, The value of R is

• 
• 
• 
• 

Kirchhoff's first and second laws for electrical circuits are consequences of

• conservation of energy

• conservation of electric charge and energy respectively

• conservation of electric charge

• conservation of electric charge

A potentiometer is an accurate and versatile device to make electrical measurements of E.M.F, because the method involves :

• Cells

• Potential gradients

• A condition of no current flow through the galvanometer

• A condition of no current flow through the galvanometer

The resistance of a wire is ‘R’ ohm. If it is melted and stretched to ‘n’ times its original length, its new resistance will be

• nR

• R/n

• n²R

• n²R

A carbon resistor of (47 ± 4.7) kΩ is to be marked with rings of different colours for its identification. The colour code sequence will be

• Violet – Yellow – Orange – Silver

• Yellow – Violet – Orange – Silver

• Green – Orange – Violet – Gold

• Yellow – Green – Violet – Gold

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 battery becomes 10 I. The value of 'n' is

• 10

• 11

• 9

• 20

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 relationship between I and n?

You are given resistance wire of length 50 cm and a battery of negligible resistance. In which of the following cases is the largest amount of heat generated?

• When the wire is connected to the battery directly

• When the wire is divided into two parts and both the parts are connected to the battery in parallel.

• When the wire is divided into four parts and all the four parts are connected to the battery in parallel.

• When only half of the wire is connected to the battery

When a voltmeter connected across the terminals of cell, measures 5 V and an ammeter connected measures 10 A. A resistance of 2 Ω is connected across the terminal of the cell. The current flowing through this resistance is

• 7.5amp

• 5.0amp

• 2.5amp

• 2.0amp

In a neon discharge tube 2.9 x 10 Ne¹⁸ ions move to be the right per second while 1.2 x 10⁸ electron move to the left per second electric charge is 1.6 x 10^-19C. The current in discharge tube is

• 0.66A towards left

• 0.66 A towards left

• 1A towards right

• Zero