JEE Questions
A resistor 'R' and 2μF capacitor in series is connected through
A resistor 'R' and 2μF capacitor in series is connected through a switch to 20 V direct supply. Across the capacitor is a neon bulb that lights up at 120 V. Calculate the value of R to make the bulb light up 5s after the switch has been closed. (log102.5 = 0.4)
- 2.7 x 106 Ω
- 1.3 x 104 Ω
- 1.7 x 105 Ω
- 3.3 x 107 Ω
If an ammeter is to be used in place of a voltmeter
If an ammeter is to be used in place of a voltmeter, then we must connect with the ammeter a
- low resistance in series
- high resistance in series
- low resistance in parallel
- high resistance in parallel
If an electron and a proton having same momenta
If an electron and a proton having same momenta enter perpendicular to a magnetic field, then
- they will move undeflected
- curved path of electron and proton will be same (ignoring the sense of revolution)
- path of proton is more curved
- curved path of electron is more curved than that of the proton
The time period of a charged particle undergoing a circular motion
The time period of a charged particle undergoing a circular motion in a uniform magnetic field is independent of its
- mass
- magnetic induction
- charge
- speed
A 3 volt battery with negligible internal resistance is connected
A 3 volt battery with negligible internal resistance is connected in a circuit as shown in the figure. The current I, in the circuit will be
- 1.5 A
- 1 A
- 2 A
- 1/3 A
The current voltage relation of diode is given by
The current voltage relation of diode is given by I = (e1000V/T - 1) mA, where the applied voltage V is in volts and the temperature T is in degree Kelvin. If a student makes an error measuring ± 0.01 V while measuring the current of 5 mA at 300 K, what will be the error in the value of current in mA?
- 0.02
- 0.2
- 0.05
- 0.5
Let C be the capacitance of a capacitor discharging through a resistor R
Let C be the capacitance of a capacitor discharging through a resistor R. Suppose t1 is the time taken for the energy stored in the capacitor to reduce to half its initial value and t2 is the time taken for the charge to reduce to one-fourth its initial value. Then the ratio t1/t2 will be
- 1/4
- 1/2
- 1
- 2
A charge Q is placed at each of the opposite corners of a square
A charge Q is placed at each of the opposite corners of a square. A charge q is placed at each of the other two corners. If the net electrical force on Q is zero, then Q/q equals
- -1
- 1
- -2√2
- -1/√2
If a charge q is placed at the centre of the line joining
If a charge q is placed at the centre of the line joining two equal charges Q such that the system is in equilibrium then the value of q is
- Q/4
- -Q/4
- Q/2
- -Q/2
On moving a charge of 20 coulombs by 2 cm, 2 J of work is done
On moving a charge of 20 coulombs by 2 cm, 2 J of work is done, then the potential difference between the points is
- 8 V
- 0.5 V
- 0.1 V
- 2 V
If θi is the inversion temperature, θn is the neutral temperature
If θi is the inversion temperature, θn is the neutral temperature, θc is the temperature of the cold junction, then
- θi - θc = 2θn
- θc - θi = 2θn
- θi + θc = θn
- θn = (θi + θc)/2
Even Carnot engine cannot give 100% efficiency because
Even Carnot engine cannot give 100% efficiency because we cannot
- eliminate friction
- reach absolute zero temperature
- prevent radiation
- find ideal sources
Three rods of Copper, Brass and Steel are welded together
Three rods of Copper, Brass and Steel are welded together to from a Y-shaped structure. Area of cross-section of each rod = 4 cm2. End of copper rod is maintained at 100°C where as ends of brass and steel are kept at 0°C.
Lengths of the copper, brass and steel rods are 46, 13 and 12 cm respectively. The rods are thermally insulated from surroundings except at ends. Thermal conductivities of copper, brass and steel are 0.92, 0.26 and 0.12 CGS units respectively. Rate of heat flow through copper rod is:
- 6.0 cal/s
- 4.8 cal/s
- 2.4 cal/s
- 1.2 cal/s
Heat given to a body which raises its temperature by 1°C is
Heat given to a body which raises its temperature by 1°C is
- specific heat
- thermal capacity
- temperature gradient
- water equivalent
Two spheres of the same material have radii 1 m and 4 m
Two spheres of the same material have radii 1 m and 4 m and temperatures 4000 K and 2000 K respectively. The ratio of the energy radiated per second by the first sphere to that by the second is
- 1:1
- 1:9
- 16:1
- 4:1
A diatomic ideal gas is used in a Carnot engine as the working substance
A diatomic ideal gas is used in a Carnot engine as the working substance. If during the adiabatic expansion part of the cycle the volume of the gas increases from V to 32 V, the efficiency of the engine is
- .99
- .75
- .50
- .25
One kg of a diatomic gas is at a pressure
One kg of a diatomic gas is at a pressure of 8 × 104 N/m2. The density of the gas is 4 kg/m3. What is the energy of the gas due to its thermal motion?
- 3 × 104 J
- 5 × 104 J
- 6 × 104 J
- 7 × 104 J
1 mole of a gas with γ = 7/5 is mixed with 1 mole of a gas with γ = 5/3
1 mole of a gas with γ = 7/5 is mixed with 1 mole of a gas with γ = 5/3, then the value of γ for the resulting mixture is
- 2/5
- 24/16
- 12/7
- 7/5
Work done in increasing the size of a soap bubble
Work done in increasing the size of a soap bubble from a radius of 3 cm to 5 cm is nearly. (Surface tension of soap solution = 0.03 Nm-1)
- 0.2π mJ
- 0.4π mJ
- 2π mJ
- 4π mJ
100 g of water is heated from 30°C to 50°C
100 g of water is heated from 30°C to 50°C ignoring the slight expansion of the water, the change in its internal energy is (specific heat of water is 4184 J/Kg/K)
- 2.1 kJ
- 4.2 kJ
- 8.4 kJ
- 84 kJ
The pressure that has to be applied to the ends of a steel wire
The pressure that has to be applied to the ends of a steel wire of length 10 cm to keep its length constant when its temperature is raised by 100°C is: (For steel, Young’s modulus is 2×1011 N m–2 and coefficient of thermal expansion is 1.1×10-5 K-1)
- 2.2 × 106 Pa
- 2.2 × 107 Pa
- 2.2 × 108 Pa
- 2.2 × 109 Pa
Water is flowing continuously from a tap having an internal diameter
Water is flowing continuously from a tap having an internal diameter 8×10-3 m. The water velocity as it leaves the tap is 0.4 ms-1. The diameter of the water stream at a distance 2×10-1 m below the tap is close to
- 7.5 × 10-3 m
- 9.6 × 10-3 m
- 3.6 × 10-3 m
- 5.0 × 10-3 m
If mass-energy equivalence is taken into account
If mass-energy equivalence is taken into account, when water is cooled to form ice, the mass of water should
- first increase then decrease
- increase
- decrease
- remain unchanged
A sonometer wire of length 1.5 m is made of steel
A sonometer wire of length 1.5 m is made of steel. The tension in it produces an elastic strain of 1%. What is the fundamental frequency of steel if density and elasticity of steel are 7.7 × 103 kg/m3 and 2.2 × 1011 N/m2 respectively?
- 178.2 Hz
- 188.5 Hz
- 200.5 Hz
- 770 Hz
A pipe of length 85 cm is closed from one end
A pipe of length 85 cm is closed from one end. Find the number of possible natural oscillations of air column in the pipe whose frequencies lie below 1250 Hz. The velocity of sound in air is 340 m/s.
- 4
- 6
- 8
- 12
A child swinging on a swing in sitting position, stands up
A child swinging on a swing in sitting position, stands up, then the time period of the swing will
- Remains same
- Decreases
- Increases
- Increase if the child is tall, decrease if the child is short
A wave y = a sin(ωt − kx) on a string meets with another wave
A wave y = a sin(ωt − kx) on a string meets with another wave producing a node at x = 0. Then the equation of the unknown wave is
- y = −a sin(ωt + kx)
- y = a sin(ωt + kx)
- y = a sin(ωt − kx)
- y = −a sin(ωt − kx)
If a spring has time period T, and is cut into n equal parts
If a spring has time period T, and is cut into n equal parts, then the time period of each part will be
- T
- T√n
- nT
- T/√n
A particle performing uniform circular motion has angular momentum
A particle performing uniform circular motion has angular momentum L. If its angular frequency is doubled and its kinetic energy halved, then the new angular momentum is
- L/4
- 4L
- L/2
- 2L
Moment of inertia of a circular wire of mass M and radius R
Moment of inertia of a circular wire of mass M and radius R about its diameter is
- (MR2)/2
- MR2
- (MR2)/4
- 2MR2
A thin uniform rod of length l and mass m is swinging
A thin uniform rod of length l and mass m is swinging freely about a horizontal axis passing through its end. Its maximum angular speed is ω. Its centre of mass rises to a maximum height of
- ωl/(6g)
- ω2l2/(2g)
- ω2l2/(6g)
- ω2l2/(3g)
A body is moved along a straight line by a machine
A body is moved along a straight line by a machine delivering a constant power. The distance moved by the body in time t is proportional to
- t1/2
- t1/4
- t3/2
- t3/4
If a body looses half of its velocity on penetrating 3 cm
If a body looses half of its velocity on penetrating 3 cm in a wooden block, then how much will it penetrate more before coming to rest?
- 1 cm
- 2 cm
- 3 cm
- 4 cm
When a rubber-band is stretched by a distance x
When a rubber-band is stretched by a distance x, it exerts a restoring force of magnitude F = ax + bx2 where a and b are constants. The work done in stretching the unstretched rubber band by L is
- aL2/2 + bL3/3
- (aL2 + bL3)/3
- aL2 + bL3
- (aL2/2 + bL3/3)/2
The height at which the acceleration due to gravity becomes g/9
The height at which the acceleration due to gravity becomes g/9 (where g = the acceleration due to gravity on the surface of the earth) in terms of R, the radius of the earth, is
- (√2)R
- R/2
- R/√2
- 2R
Two bodies of masses m and 4m are placed at a distance r
Two bodies of masses m and 4m are placed at a distance r. The gravitational potential at a point on the line joining them where the gravitational field is zero is
- zero
- -4Gm/r
- -6Gm/r
- -9Gm/r
If suddenly the gravitational force of attraction between Earth
If suddenly the gravitational force of attraction between Earth and a satellite revolving around it becomes zero, then the satellite will
- move tangentially to the originally orbit in the same velocity
- continue to move in its orbit with same velocity
- become stationary in its orbit
- move towards the earth
The escape velocity for a body projected vertically upwards
The escape velocity for a body projected vertically upwards from the surface of earth is 11 km/s. If the body is projected at an angle of 45° with the vertical, the escape velocity will be
- 11/√2 m/s
- 11√2 km/s
- 22 km/s
- 11 km/s
The kinetic energy needed to project a body of mass
The kinetic energy needed to project a body of mass m from the earth surface (radius R) to infinity is
- mgR
- 2mgR
- mgR/4
- mgR/2
A radar has a power of 1 Kw and is operating at a frequency of 10 GHz
A radar has a power of 1 Kw and is operating at a frequency of 10 GHz. It is located on a mountain top of height 500 m. The maximum distance upto which it can detect object located on the surface of the earth (Radius of earth = 6.4 x 106 m) is
- 80 km
- 64 km
- 40 km
- 16 km
The escape velocity of a body depends upon mass as
The escape velocity of a body depends upon mass as
- m0
- m1
- m2
- m3
The mass of a spaceship is 1000 kg. It is to be launched
The mass of a spaceship is 1000 kg. It is to be launched from the earth's surface out into free space. The value of 'g' and 'R' (radius of earth) are 10 m/s2 and 6400 km respectively. The required energy for this work will be
- 6.4 X 108 Joules
- 6.4 X 109 Joules
- 6.4 X 1010 Joules
- 6.4 X 1011 Joules
When forces F1, F2, F3 are acting on a particle of mass m
When forces F1, F2, F3 are acting on a particle of mass m such that F2 and F3 are mutually perpendicular, then the particle remains stationary. If the force F1 is now removed then the acceleration of the particle is
- F1/m
- (F2 - F3)/m
- (F2F3)/(mF1)
- F2/m
Two forces are such that the sum of their magnitudes is 18 N
Two forces are such that the sum of their magnitudes is 18 N and their resultant is 12 N which is perpendicular to the smaller force. Then the magnitudes of the forces are
- 10 N, 8 N
- 12 N, 6 N
- 13 N, 5 N
- 16 N, 2 N
A spring balance is attached to the ceiling of a lift
A spring balance is attached to the ceiling of a lift. A man hangs his bag on the spring and the spring reads 49 N, when the lift is stationary. If the lift moves downward with an acceleration of 5 m/s2, the reading of the spring balance will be
- 15 N
- 24 N
- 49 N
- 74 N
A mass ‘m’ is supported by a massless string wound around a uniform
A mass ‘m’ is supported by a massless string wound around a uniform hollow cylinder of mass m and radius R. If the string does not slip on the cylinder, with what acceleration will the mass fall on release?
- g
- 5g/6
- g/2
- 2g/3
An object moving with a speed of 6.25 m/s
An object moving with a speed of 6.25 m/s, is decelerated at a rate given by dν/dt = 2.5√ν, where ν is the instantaneous speed. The time taken by the object, to come to rest, would be
- 8 s
- 4 s
- 2 s
- 1 s
A particle is moving with velocity v = K(yi + xj)
A particle is moving with velocity v = K(yi + xj), where K is a constant. The general equation for its path is
- xy = constant
- y2 = x + constant
- y2 = x2 + constant
- y = x2 + constant
A water fountain on the ground sprinkles water all around it
A water fountain on the ground sprinkles water all around it. If the speed of water coming out of the fountain is v, the total area around the fountain that gets wet is
- πv4/2g2
- πv2/g2
- πv4/g2
- πv2/g
A boy can throw a stone up to a maximum height of 10 m
A boy can throw a stone up to a maximum height of 10 m. The maximum horizontal distance that the boy can throw the same stone up to will be
- 10 m
- 20√2 m
- 20 m
- 10√2 m
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