The candela is the luminous intensity, in a given direction, of a source that emits monochromatic radiation of frequency \( 'A' \times 10^{12} \, \text{hertz} \) and that has a radiant intensity in that direction of \( \frac{1}{'B'} \, \text{watt per steradian} \). 'A' and 'B' are respectively:
- 540 and \( \frac{1}{683} \)
- 540 and 683
- 450 and \( \frac{1}{683} \)
- 450 and 683
The Correct Option is B
Approach Solution - 1
The question asks about the definition of the candela, which is one of the seven base units in the International System of Units (SI). A candela is defined as the luminous intensity, in a given direction, of a source that emits monochromatic radiation.
Let’s break down the given information:
- The frequency of the monochromatic radiation is given as \( A \times 10^{12} \, \text{hertz} \).
- The radiant intensity in that direction is \( \frac{1}{B} \, \text{watt per steradian} \).
The problem provides options for values of A and B. To find the correct answer, we need to recall the standard definition:
The candela is defined by the frequency of radiation being 540 × 1012 hertz and has a radiant intensity of 1/683 watt per steradian.
Thus, the correct values for A and B from the options given are:
- Frequency: 540 (in terms of 540 × 1012 hertz)
- Radiant Intensity: 683 (where the radiant intensity is defined as \( \frac{1}{683} \, \text{watt per steradian} \))
Therefore, the correct option is 540 and 683.
The incorrect options can be discounted because:
- Options with 450 do not match the standard frequency for defining a candela.
- The option with \( \frac{1}{683} \) as B does not match the radiant intensity needed for a standard candela.
Thus, the correct answer is 540 and 683 according to the SI unit definition of candela.
Approach Solution -2
The definition of candela specifies:
- $A = 540 \times 10^{12}$ hertz is the frequency of the monochromatic light.
- $B = 683$ is the luminous efficacy in terms of watts per steradian.
These values are based on the standard SI definition of candela.
Top JEE Main Chemistry Questions
What will be the equilibrium constant of the given reaction carried out in a \(5 \,L\) vessel and having equilibrium amounts of \(A_2\) and \(A\) as \(0.5\) mole and \(2 \times 10^{-6}\) mole respectively?
The reaction : \(A_2 \rightleftharpoons 2A\)- At equilibrium the concentrations of and in a sealed vessel at . What will be for the reaction
- Find out the major products from the following reactions
Cobalt chloride when dissolved in water forms pink colored complex $X$ which has octahedral geometry. This solution on treating with cone $HCl$ forms deep blue complex, $\underline{Y}$ which has a $\underline{Z}$ geometry $X, Y$ and $Z$, respectively, are
- The correct order of atomic radii is:
Top JEE Main Photoelectric Effect Questions
Top JEE Main Questions
- In a hydrogen like atom, when an electron jumps from the $M$ - shell to the $L$ - shell, the wavelength of emitted radiation is $\lambda$. If an electron jumps from $N$-shell to the $L$-shell, the wavelength of emitted radiation will be :
- Two masses $m$ and $\frac{m}{2}$ are connected at the two ends of a massless rigid rod of length $l$. The rod is suspended by a thin wire of torsional constant $k$ at the centre of mass of the rod-mass system(see figure). Because of torsional constant $k$, the restoring torque is $\tau =k\theta$ for angular displacement $\theta$. If the rod is rota ted by $\theta_0$ and released, the tension in it when it passes through its mean position will be:
What will be the equilibrium constant of the given reaction carried out in a \(5 \,L\) vessel and having equilibrium amounts of \(A_2\) and \(A\) as \(0.5\) mole and \(2 \times 10^{-6}\) mole respectively?
The reaction : \(A_2 \rightleftharpoons 2A\)- The value of is
- The number of terms of an is even. The sum of the odd terms is and of the even terms is . The last term exceeds the first by . Then the number of terms in the series is ______.