WAEC SSCE - Physics - 2001

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The time rate of change of momentum is called "force". Force is a vector quantity that causes an object to accelerate or change its velocity. When a force acts on an object for a certain amount of time, it produces a change in the object's momentum, which is called impulse. Therefore, force can also be defined as the rate of change of momentum, that is, the amount of impulse produced per unit of time.

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When lamps are connected in parallel, each lamp has the same voltage across it. Therefore, the potential difference across each of the three lamps is 250V. The power of each lamp is given as 100W. We know that power (P) is equal to voltage (V) multiplied by current (I), i.e., P = VI. Therefore, the current through each lamp can be calculated as I = P/V = 100/250 = 0.4 A. Since the lamps are connected in parallel, the total current in the circuit is the sum of the currents through each lamp. Hence, the total current in the circuit is 3 times the current through one lamp, which is 3 x 0.4 A = 1.2 A. Therefore, the correct option is 1.2A.

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The gravitational force between two particles is given by the formula F = Gm₁m₂/r², where G is the gravitational constant, m₁ and m₂ are the masses of the particles, and r is the distance between them. In this case, the distance between the particles is initially 0.10m and the force is 10N. If the distance is increased to 0.20m, we can use the formula to calculate the new force. Let's assume that the masses of the particles remain constant. The distance between them is doubled, so the new distance is 2r = 0.20m. Plugging this into the formula and solving for the new force, we get: F' = Gm₁m₂/(2r)² = Gm₁m₂/4r² Since the masses of the particles and the gravitational constant are constants, the only thing that has changed is the distance between the particles. Therefore, the new force is proportional to 1/r². Since r has doubled, the new force will be (1/2)² = 1/4 of the original force. So, the new force is: F' = (1/4)F = (1/4)10N = 2.5N Therefore, the magnitude of the new force is 2.5N. Option (C) is the correct answer.

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The physical quality that affects the saturated vapour pressure of a liquid is temperature. Saturated vapour pressure is the pressure exerted by the vapour present in a system at equilibrium with its condensed phase, usually a liquid. As temperature increases, the average kinetic energy of the liquid molecules increases, causing more molecules to escape from the liquid phase and enter the gas phase. This leads to an increase in the number of gas molecules, which in turn results in an increase in pressure. As a result, the saturated vapour pressure of a liquid increases with increasing temperature, and decreases with decreasing temperature. Therefore, temperature is the correct answer. The other options - volume, mass, and density - do not directly affect the saturated vapour pressure of a liquid.

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The Earth's magnetic field has a north and south pole, and it is tilted with respect to the Earth's rotational axis. This means that at different points on the Earth's surface, the magnetic field has different characteristics. The magnetic equator is an imaginary line that circles the Earth, and it is the point where the magnetic field is horizontal. At Jos in Nigeria, the magnetic equator passes through, and this means that the magnetic field is horizontal at this point. Therefore, the angle of dip (the angle between the magnetic field lines and the Earth's surface) is zero.

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The force exerted on the block is 3N, and the block is at rest, meaning that the force of friction is equal in magnitude and opposite in direction to the applied force. Therefore, the friction force on the block is 3N. Answer: 3.0N

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The equation that represents the distance x, travelled by a body moving on a straight road with a constant speed is "x = Ut". In this equation, "U" represents the initial velocity of the body and "t" represents the time taken to cover the distance "x". Since the body is moving with a constant speed, its velocity remains the same throughout the journey and can be represented by "U". Therefore, the distance covered by the body can be calculated by multiplying the velocity "U" with the time taken "t", which is given by the equation "x = Ut". The other given equations represent the distance covered by a body in different scenarios like constant acceleration, initial velocity with constant acceleration, etc.

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A screw jack is a simple machine used to lift heavy loads with little effort. The velocity ratio of a screw jack is defined as the ratio of the distance moved by the effort (Tommy bar) to the distance moved by the load (car). In this case, the car is raised through a vertical height of 25cm by turning the Tommy bar through 50 revolutions. The distance moved by the effort is the circumference of the circle traced out by the end of the Tommy bar, which is given by: circumference = 2πr = 2 x 3.142 x 0.12m = 0.754m (approx.) Since the Tommy bar is turned through 50 revolutions, the total distance moved by the effort is: distance moved by effort = 0.754m x 50 = 37.7m (approx.) Therefore, the velocity ratio is: velocity ratio = distance moved by effort / distance moved by load = 37.7m / 0.25m = 150.8 (approx.) So the approximate velocity ratio of the jack is 151, which is closest to.

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Convex spherical mirrors are preferred to plane mirrors as driving mirrors because they provide a wider field of view. Convex mirrors are curved outward and the reflected light rays diverge, resulting in a smaller image that appears farther away. This makes it easier for drivers to see objects behind them and in their blind spots. The wider field of view provided by convex mirrors is particularly useful for large vehicles such as buses and trucks, which have larger blind spots than smaller cars.

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Electrical resistance is a property of a material to oppose the flow of electrical current through it. When electrical current flows through a conductor, some of the electrical energy is converted into other forms of energy. One of the forms of energy that can be generated is heat energy, which is the result of collisions between the electrons and the atoms in the material. This is known as Joule heating, and the amount of heat generated is proportional to the resistance of the material and the square of the current flowing through it. Therefore, when electrical energy flows through a material with resistance, some of the energy is converted into heat energy due to the resistance of the material.

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The physical processes of evaporation, thermal conduction, radiation of heat, and convectional current of fluids can all be explained by the molecular theory of matter. The theory explains that all matter is made up of tiny particles (atoms or molecules) which are constantly in motion. The motion of these particles can cause heat transfer through conduction, convection, and radiation. Evaporation is a process where some of the particles at the surface of a liquid have enough energy to escape and become a gas. Therefore, all the options listed can be explained by the molecular theory of matter.

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The material used for constructing the core of an electromagnet is iron. An electromagnet is made by wrapping a coil of wire around a ferromagnetic core. When electric current flows through the wire, it creates a magnetic field around the wire. The ferromagnetic core helps to increase the strength of the magnetic field created by the current flowing through the wire. Iron is a good material for the core of an electromagnet because it is a ferromagnetic material that is easily magnetized and demagnetized. It also has a high magnetic permeability, which means it can conduct magnetic flux effectively.

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The pressure, volume, and temperature of an ideal gas are related by the ideal gas law, which is given by: P V = n R T where P is the pressure, V is the volume, n is the number of moles of gas, R is the gas constant, and T is the absolute temperature. If the volume of the gas remains constant, then the ideal gas law becomes: P = n R T / V Since the mass of the gas is constant, the number of moles n is also constant. Therefore, we can write: P/T = constant This means that the pressure of the gas is directly proportional to its temperature, when the volume is constant. To solve the problem, we can use the above formula to find the constant, and then use it to find the pressure at the new temperature: P1 / T1 = P2 / T2 where P1 is the initial pressure, T1 is the initial temperature, P2 is the final pressure, and T2 is the final temperature. Converting the temperatures to kelvin scale: T1 = 273 - 13 = 260 K T2 = 273 + 247 = 520 K Substituting the values: 500 / 260 = P2 / 520 Solving for P2: P2 = (500 / 260) x 520 = 1000 Nm^-2 Therefore, the pressure of the gas at the new temperature is 1000 Nm^-2. The correct option is: 1000Nm^-2.

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Electrons, which are usually considered as particles, can also exhibit wave-like properties, a concept known as wave-particle duality. When electrons are passed through crystals, their wave-like nature allows them to diffract, meaning they bend and scatter as they encounter the atoms in the crystal. This is similar to the way light diffracts when it passes through a narrow opening or encounters an obstacle. Therefore, the correct answer is that electrons passing through crystals are diffracted because they possess wave properties.

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The apparent weight of a body in a fluid is equal to the weight of the fluid displaced by the body. Using this principle, we can calculate the volume of the body as follows: Let V be the volume of the body Density of water = 1000kgm^-3 Weight of the body in air = 96N Weight of the body in water = 32N We know that: Weight of the body in air - Weight of the body in water = Upthrust = Weight of the water displaced Therefore, 96N - 32N = Weight of the water displaced 64N = Weight of the water displaced Weight of water displaced = Volume of body x Density of water x g 64N = V x 1000kgm^-3 x 10ms^-2 V = 64N / (1000kgm^-3 x 10ms^-2) V = 6.4 x 10^-3m³ Therefore, the volume of the body is 6.4 x 10^-3m³. Answer is correct.

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The power of an electrical appliance can be calculated by the formula P = V\(^2\)/R, where P is the power in watts, V is the voltage in volts, and R is the resistance in ohms. In this case, the bulb is rated 60W and 220V. So, we can rearrange the formula to find the resistance: R = V\(^2\)/P. Substituting the values gives us: R = 220\(^2\)/60. Evaluating this expression gives us: R = 806.7\(\Omega\). Therefore, the resistance of the filament when the bulb is operating normally is 806.7\(\Omega\). Note: It is important to remember that the actual resistance of the filament may vary due to factors such as temperature, age, and manufacturing tolerances.

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The amount of heat given out or absorbed when a substance changes its state at a constant temperature is known as latent heat. This means that even though the temperature remains constant during the change of state, heat is still being absorbed or released. For example, when ice is melted into water or water is evaporated into steam, there is no change in temperature, but heat is still absorbed by the substance during the change of state. The latent heat is specific to the substance and the change of state, and can be calculated by multiplying the mass of the substance by the specific latent heat of the substance for the particular change of state.

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The correct option is "magnetic lines of force are closely packed together at neutral point". This statement is incorrect because neutral points are regions where the magnetic field is zero, and hence, there are no magnetic lines of force in these regions. Magnetic lines of force are an imaginary concept used to represent the direction and intensity of magnetic fields. They are assumed to be continuous and form closed loops, and are said to originate from the north pole and terminate at the south pole of a magnet. They also represent the path along which a free north pole would move in the presence of a magnetic field. Magnetic lines of force do not cross one another, and the presence of magnetic lines of force in a region indicates the presence of a magnetic field.

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Humidity is used to describe the amount of water vapour present in the atmosphere. It is the measure of the water vapour content in the air, which can affect how comfortable we feel in a particular environment. Humidity can be measured in various ways, including absolute humidity, relative humidity, and specific humidity. Knowing the humidity level is important for a range of applications, from weather forecasting to indoor comfort control.

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When surface waves travelling in deep water meet a shallow water boundary, they experience a change in speed and direction. This is known as refraction. The speed of the waves is dependent on the medium they are travelling through, so when they enter shallow water, their speed will change. We can use Snell's law, which states that the ratio of the sines of the angles of incidence and refraction is equal to the ratio of the velocities in the two media. In this case, we have: \begin{align*} \frac{\sin i}{\sin r} &= \frac{v_i}{v_r} \\ \frac{\sin 45}{\sin 30} &= \frac{15}{v_r} \\ \frac{\sqrt{2}}{0.5} &= \frac{15}{v_r} \\ v_r &= \frac{15}{\frac{\sqrt{2}}{0.5}} \\ v_r &= 10.6\text{ms}^{-1} \end{align*} Therefore, the speed of the waves in shallow water is approximately 10.6ms^-1. The correct option is (c) 10.6ms^-1.

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When an object appears a certain color, it is because it reflects that particular color of light and absorbs all other colors. Therefore, if a piece of cloth appears green in sunlight, it means that it reflects green light and absorbs all other colors. When the same piece of cloth is held in red light, it will appear black. This is because the red light being shone on the cloth contains only red light waves, and the cloth will absorb all the red light, as it does not reflect red light. Therefore, it appears black, as there is no reflected color for our eyes to see.

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The maximum acceleration of a particle in simple harmonic motion is given by the product of the square of the angular frequency and the displacement of the particle from the equilibrium position. That is, a_max = -ω²A Where, A is the amplitude of the particle, and ω is the angular frequency. Substituting the given values, we get: a_max = - (10 rad/s)² x 0.05 m a_max = - 5 m/s² or 5 ms^-2 Since the maximum acceleration is a scalar quantity, we take its magnitude, which is simply 5 ms^-2. Therefore, the correct option is 5.00ms^-2.

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In an elastic collision, both kinetic energy and momentum are conserved. This means that the total kinetic energy before the collision is equal to the total kinetic energy after the collision, and the total momentum before the collision is equal to the total momentum after the collision. There is no loss of kinetic energy or momentum in an elastic collision. Therefore, the statement "both kinetic energy and momentum are conserved" is correct. The other statements are incorrect as they imply a loss of either kinetic energy or momentum in an elastic collision, which is not the case.

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