The device that works on the principle of electromagnetic induction is
a.
electric generator
Correct Answer
b.
electric heater
c.
electric motor
d.
electric fan
Step-by-Step AI Explanation
Verified Method
An electric generator works on the principle of electromagnetic induction (Faraday's law), where mechanical energy is converted into electrical energy by rotating a coil in a magnetic field. An electric motor (c) and fan (d) typically use the magnetic effect of current to produce motion, and an electric heater (b) works on the heating effect of electric current.
Q42mcq
An electric lamp whose resistance is 30 $\Omega$ and a conductor of 6 $\Omega$ resistance are connected in series to 9V battery as shown in the figure. The total current flowing in the circuit is
a.
4 A
b.
36 A
c.
0.25 A
Correct Answer
d.
0.6 A
Step-by-Step AI Explanation
Verified Method
In a series circuit, the total resistance $R_{total} = R_1 + R_2$. Given $R_1 = 30 \, \Omega$ and $R_2 = 6 \, \Omega$, $R_{total} = 30 + 6 = 36 \, \Omega$. Using Ohm's Law $V = I \cdot R$, the current $I = V / R_{total} = 9 \text{ V} / 36 \, \Omega = 0.25 \text{ A}$.
Q43mcq
The inner wall of the solar cooker is painted black because this
a.
reflects light
b.
converges solar radiations
c.
prevents from rusting
d.
absorbs more heat
Correct Answer
Step-by-Step AI Explanation
Verified Method
Black surfaces are excellent absorbers of heat radiation. Painting the inner wall of a solar cooker black ensures that the solar energy falling on it is absorbed efficiently to cook the food inside, rather than being reflected (a).
Q44mcq
The metal used in the filament of an electric bulb is
a.
manganese
b.
tungsten
Correct Answer
c.
nickel
d.
chromium
Step-by-Step AI Explanation
Verified Method
Tungsten is used for the filament of an electric bulb because it has a very high melting point ($3380^\circ \text{C}$), allowing it to glow at high temperatures without melting, and it does not oxidize readily.
Q45mcq
A rectangular coil of copper wire is rotated in a magnetic field. The direction of the induced current changes once in each
a.
two revolutions
b.
one revolution
c.
half revolution
Correct Answer
d.
one-fourth revolution
Step-by-Step AI Explanation
Verified Method
In a DC generator (or simple rotating coil), the current changes direction every half revolution as the sides of the coil swap positions relative to the magnetic poles, which is why a split-ring commutator is often used to ensure unidirectional output.
Q46mcq
The focal length of a lens is + 0.50 m. The power of the lens and type are
a.
+ 2.0 D and convex lens
Correct Answer
b.
+ 2.0 D and concave lens
c.
– 2.0 D and concave lens
d.
– 2.0 D and convex lens
Step-by-Step AI Explanation
Verified Method
The power of a lens is defined as $P = 1/f$ (where $f$ is in meters). Given $f = +0.50 \text{ m}$, $P = 1 / 0.50 = +2.0 \text{ D}$. A positive focal length indicates a convex (converging) lens.
Q47mcq
A device used to change the resistance in the electric circuit is
a.
voltmeter
b.
ammeter
c.
galvanometer
d.
rheostat
Correct Answer
Step-by-Step AI Explanation
Verified Method
A rheostat (or variable resistor) is specifically designed to change the resistance in an electric circuit to regulate the flow of current. Ammeters and voltmeters are measuring devices, not control devices.
Q48mcq
The magnetic field lines inside a solenoid are in the form of parallel straight lines. The reason for this is, the magnetic field inside the solenoid is
a.
very high
b.
uniform
Correct Answer
c.
zero
d.
produced by electric current
Step-by-Step AI Explanation
Verified Method
Inside a current-carrying solenoid, the magnetic field lines are parallel and equidistant, which is the physical representation of a uniform magnetic field.
Q49mcq
The nature and the size of the image formed when an object is kept between the principal focus $F_1$ and optical centre O of a convex lens are
a.
virtual, erect and enlarged
Correct Answer
b.
real, inverted and small size
c.
virtual, inverted and small size
d.
real, inverted and enlarged
Step-by-Step AI Explanation
Verified Method
When an object is placed between the principal focus F1 and the optical centre O of a convex lens, it acts as a magnifying glass. The image formed is virtual, erect, and enlarged, and it appears on the same side as the object. Options B, C, and D are incorrect because they describe images formed in different positions (e.g., real images are formed beyond the focus, whereas this specific position yields a virtual image).
Q50mcq
The device that converts electrical energy into mechanical energy is
a.
electric generator
b.
solar cell
c.
dry cell
d.
electric motor
Correct Answer
Step-by-Step AI Explanation
Verified Method
An electric motor is a device that converts electrical energy into mechanical energy by using the magnetic effect of current. An electric generator does the opposite (mechanical to electrical), while dry cells and solar cells are sources of electrical energy, not converters of electrical into mechanical energy.
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Observe the following table:
| Material medium | Refractive index |
| :--- | :--- |
| P | 1.52 |
| Q | 1.44 |
| R | 2.42 |
| S | 1.33 |
In which material medium the speed of light is very high ?
a.
Q
b.
P
c.
S
d.
R
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Observe the following chemical reactions :
Fe + $CuSO_4$ $\to$ $FeSO_4$ + Cu
Zn + $FeSO_4$ $\to$ $ZnSO_4$ + Fe
The decreasing order of reactivity of the metals in the above reactions is
a.
Zn > Fe > Cu
b.
Fe > Cu > Zn
c.
Zn > Cu > Fe
d.
Cu > Fe > Zn
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A pot that has growing seedling is kept in a dark room. A burning candle is placed near it for a few days. The top part of the seedling bends towards the light of burning candle. This is
a.
Chemotropism
b.
Phototropism
c.
Geotropism
d.
Hydrotropism
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