Question
Obtain the magnification by lens after giving the definition.
✓
Answer
→The ratio of the size of the image obtained by lens to that of the object is called magnification.
$m=\frac{h^{\prime}}{h}......(1)$
→As shown in figure AB is an object and its image is $A ^{\prime} B ^{\prime}$.
→From figure $\triangle ABP$ and $\triangle A ^{\prime} B ^{\prime} P$ are similar triangles.
$\therefore \quad \frac{ A ^{\prime} B ^{\prime}}{ AB }=\frac{ B ^{\prime} P }{ BP }$
→$\begin{array}{lll}\text { But, } & A ^{\prime} B ^{\prime}=-h^{\prime} & AB =h \\ & B^{\prime} P =v & BP =-u\end{array}$
→Substituting these values in above equation,
$\begin{array}{l}\therefore \frac{-h^{\prime}}{h}=-\frac{v}{u} \\\therefore \frac{h^{\prime}}{h}=\frac{v}{u}......(2)\end{array}$
→Comparing equation (1) and (2),
$\therefore m=\frac{v}{u}$
→If the image formed by lens is virtual then magnification $(m)$ is positive and if the image formed by lens is real then magnification $(m)$ is negative.
Need a full question paper?
Generate a complete, print-ready paper with questions like this in minutes — across 16+ boards, with answer keys.
Explore more
Similar questions
A given galvanometer is to be converted into (i) an ammeter (ii) a milliammeter (iii) a voltmeter. In which case will the required resistance be (i) least (ii) highest and why?
A current of 5.0A exists in the circuit shown in the figure. The wire PQ has a length of 50cm and the magnetic field in which it is immersed has a magnitude of 0.20T. Find the magnetic force acting on the wire PQ.
In the given figure, voltage across the ends of inductor ( L ) and resistor ( R ) is 120 V and 90 V respectively. The root mean square value of the current is 3 A. Calculate :
(i) impedance of the circuit and (ii) phase difference between voltage and current.
(i) impedance of the circuit and (ii) phase difference between voltage and current.
A semi-circular arc of radius 20cm carries a current of 10A. Calculate the magnitude of magnetic field at the centre of the arc.
- Define ‘activity’ of a radioactive substance.
- Two different radioactive elements with half lives T1 and T2 have N1 and N2 undecayed atoms respectively present at a given instant. Derive an expression for the ratio of their activities at this instant in terms of N1 and N2.
Three equal charges, 2.0 × 10-6C each, are held fixed at the three corners of an equilateral triangle of side 5cm. Find the Coulomb force experienced by one of the charges due to the rest two.
Define atomic mass unit.
Calculate the temperature at which the resistance of a conductor becomes 20% more than its resistance at 27°C. The value of the temperature coefficient of resistance of the conductor is $2.0 \times 10\frac{-4}{\text{K}}.$
→In the given circuit, with steady current, calculate the potential difference across the capacitor and the charge stored in it.
A circular coil of radius $10 cm , 500$ turns and resistance $2 \Omega$ is placed with its plane perpendicular to the horizontal component of the earth's magnetic field. It is rotated about its vertical diameter through $180^{\circ}$ in $0.25 s$. Estimate the magnitudes of the emf and current induced in the coil. Horizontal component of the earth's magnetic field at the place is $3.0 \times 10^{-5} T$.
→