Physics Foundations: Class 8–9 Concepts (Electricity, Magnetism, Pressure, Light, Motion, Forces, Energy): 30 MCQs with answers

D · It deflects because the wire produces a magnetic field.

A current-carrying wire produces a magnetic field around it, which deflects a nearby compass needle — this is the Oersted experiment.

C · Concentric circles perpendicular to the wire

The magnetic field forms concentric circles in a plane perpendicular to the wire.

C · A bar magnet

A solenoid behaves like a bar magnet with a north and south pole when current flows through it.

A · The chemical effect

Electroplating uses the chemical effect of current to deposit one metal onto another.

C · Air moves from high pressure to low pressure.

Wind is produced when air moves from a region of high pressure to a region of low pressure.

C · A rotating low-pressure storm system

A cyclone is a huge rotating low-pressure storm system.

B · Virtual, upright, same size

A plane mirror forms a virtual, upright, same-size image.

A · True

The magnetic effect of current was discovered by Oersted when a compass needle deflected near a current-carrying wire.

A · It becomes a magnet

When current flows through a wire, it generates a magnetic field around it, making the wire behave like a magnet.

C · Concentric circles

The magnetic field around a straight current-carrying wire forms concentric circles in a plane perpendicular to the wire.

D · To break the circuit due to high current

A fuse melts and breaks the circuit when the current is too high, preventing overheating and potential hazards.

C · Pressure differences

Wind moves from high pressure to low pressure areas, driven by differences in atmospheric pressure.

D · Convex mirror

A plane mirror forms a virtual, upright image that is the same size as the object.

B · It rises

Heated air becomes less dense and rises, which contributes to the formation of winds and storms.

D · It increases heat produced

Increasing the current in a wire increases the heat produced due to more collisions between electrons and atoms.

D · It causes air to spiral

The Coriolis effect, due to Earth's rotation, causes the incoming air to spiral rather than move straight into a low-pressure center.

D · Concave lens

A concave lens diverges light, spreading it outwards, which is useful for correcting short-sightedness.

D · A push or pull

A force is defined as a push or pull that can change the state of motion of an object.

C · It is magnetic only while current flows.

An electromagnet can be switched on and off because it is magnetic only while current flows.

B · It can be switched on and off with current.

The on/off control of an electromagnet is what makes it useful in bells, cranes, and loudspeakers.

C · The filament has high resistance, so it heats up more.

The heating effect depends on resistance; the filament has high resistance and glows, while connecting wires have low resistance.

D · The heating effect

A fuse uses the heating effect: excess current produces enough heat to melt the fuse and break the circuit.

C · Unequal heating of the Earth's surface by the Sun

Unequal solar heating creates pressure differences that drive winds.

C · The Coriolis effect due to Earth's rotation makes them spiral.

The Coriolis effect, caused by Earth's rotation, makes incoming air spiral rather than move straight in.

A · Anticlockwise

In the Northern Hemisphere the Coriolis effect makes cyclone winds spiral anticlockwise; in the Southern Hemisphere they spiral clockwise.

D · It weakens because it loses its moisture supply.

Cyclones weaken over land because they lose the moisture supply that keeps the storm going.

D · 0.2 T

The magnetic field strength is directly proportional to the current. If the current doubles from 5 A to 10 A, the magnetic field strength also doubles from 0.1 T to 0.2 T.

D · 0.3 T

The magnetic field inside a solenoid is given by the formula \( B = \mu_0 rac{N \cdot I}{L} + B_{external} \). Assuming the solenoid's internal field is dominant, the total magnetic field is \( B = \mu_0 \cdot rac{200 \cdot 3}{L} \). For simplicity, if we assume \( L \) is such that \( \mu_0 \) gives 0.3 T for 3 A, t…

A · 80 J

The heat generated can be calculated using the formula \( Q = I^2 \cdot R \cdot t \). Thus, \( Q = (2^2) \cdot 4 \cdot 10 = 16 \cdot 10 = 160 \, ext{J} \). Hence, the heat generated is 80 J.

B · 60 cm on the opposite side

Using the lens formula \( rac{1}{f} = rac{1}{v} - rac{1}{u} \), where \( f = 20 \, ext{cm} \) and \( u = -30 \, ext{cm} \), we find \( v = 60 \, ext{cm} \) on the opposite side of the lens.