1. A non-conducting slid sphere of radius R is uniformly charged. The magnitude of the electric field due to the sphere at a distance r from its centre :

(A) increases as r increases for r < R

(B) decreases as r increases for 0 < r < ∞

(C) decreases as r increases for R < r < ∞

(D) is discontinuous at r = R

2. A transverse sinusoidal wave of amplitude a, wavelength l and frequency f is travelling on a stretched string. The maximum speed of any point on the string is v/10, where v is the speed of propagation of the wave. If a = 10^–3 m and v = 10 m/s, then λ and f are given by :

(A) λ = 2π × 10^–2 m,f = 10³ Hz/2π (B)λ = 10^–3 m, f = 10³ Hz/2π

(C) λ = 2π × 10^–2 m, f = 10

^{4}Hz (D)λ = 10^–3 m, f = 10

^{4}Hz

3. A black body is at a temperature of 2880 K. The energy of radiation emitted by this object with wavelength between 499 nm and 500 nm is U1, between 999 nm and 1000 nm is U2 and between 1499 nm and 1500 nm is U3. The Wein constant, b = 2.88 × 10^6 nm–K. Then :

(A) U1 = 0 (B) U3= 0

(C) U1 > U2 (D) U2 > U1

4. The SI unit of the inductance, the henry can be written as:

(A) Weber/ampere (B) Volt-second/ampere

(C) Joule/(ampere)² (D) ohm-second

5. Two very long straight parallel wires carry steady currents I and –I respectively. The distance between the wires is d. At a certain instant of time, a point charge q is at a point equidistant from the two wires in the plane of the wires. Its instantaneous velocity

**v**is perpendicular to this plane. The magnitude of the force due to the magnetic field acting on the charge at this instant is :

(A) (μ° Iqv) / 2πd (B) (μ° Iqv) / πd

(C) (2μ° Iqv) / πd (D) 0

1998 JEE

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